- The document discusses different types of radar transmitters, including high-power oscillators and high-power amplifiers. It describes how the transmitter design impacts whether a radar system is non-coherent, coherent, or pseudo-coherent.
- A pseudo-coherent radar uses a self-oscillating transmitter like a magnetron that produces pulses with random phases. It aims to achieve coherence by locking a reference oscillator in the receiver to the transmitter frequency during the pulse to enable Doppler detection.
- Truly coherent radars use a power amplifier transmitter driven by a stable oscillator. This ensures each pulse starts with the same phase, allowing differentiation of small velocity differences through Doppler processing.
A turnstile antenna, or crossed-dipole antenna,[1] is a radio antenna consisting of a set of two identical dipole antennas mounted at right angles to each other and fed in phase quadrature; the two currents applied to the dipoles are 90° out of phase.[2][3] The name reflects the notion the antenna looks like a turnstile when mounted horizontally. The antenna can be used in two possible modes. In normal mode the antenna radiates horizontally polarized radio waves perpendicular to its axis. In axial mode the antenna radiates circularly polarized radiation along its axis.
Radar and secondary radar systems use radio waves to detect objects and provide essential information to operators. Radar works by transmitting radio waves that bounce off targets and are received, allowing calculation of range and position. Secondary radar requires aircraft to carry transponders that respond to interrogations by transmitting a coded reply signal carrying additional data like identification and altitude. This improves detection range and allows transmission of emergency information.
This document discusses different types of pulsed radar systems and moving target indication techniques. It describes coherent and non-coherent radar systems, with coherent systems able to use echo phase information to determine target range and velocity. It then focuses on phase processing moving target indication using a delay-line canceller. The canceller subtracts delayed and undelayed video signals, causing signals from stationary targets to cancel out while signals from moving targets remain. This allows the radar display to only show moving targets.
Cycloconverters are used to convert AC power directly to AC power of variable magnitude and frequency. They have four main advantages over conventional AC to DC to AC conversion: they do not require an intermediate DC link, allow bidirectional power flow, can produce high quality sine waves at low frequencies without filters, and are line commutated without a separate commutation circuit. Cycloconverters are commonly used to drive large induction and synchronous motors at frequencies from 0-20Hz, such as in cement mill, ship propulsion, rolling mill, and mine applications. However, they have disadvantages of not allowing smooth stepless frequency control, producing more distortion at low frequencies, and having a more complex control circuit design.
Frequency hopping spread spectrum (FHSS) works by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. The transmitter hops from one frequency to another, transmitting short bursts of information on each channel in turn. The receiver hops in synch to receive the signals. This makes the signal resistant to interference and jamming as an eavesdropper would need to know the hop sequence to intercept the entire message coherently.
Oscillators generate an output signal without an input signal by converting DC power to AC power. They produce periodic waveforms like sine, square, triangle, and sawtooth waves. The Wien bridge oscillator is a two-stage RC coupled amplifier circuit that is stable at its resonant frequency. It uses a feedback circuit of series and parallel RC networks to produce a phase shift. Monostable multivibrators have one stable and one quasi-stable state. They switch to the quasi-stable state when triggered externally and return to the stable state after a set time period determined by resistor-capacitor values in the circuit.
The document discusses different types of antennas used for radio transmission and reception. It categorizes antennas into several groups: log periodic antennas, wire antennas, travelling wave antennas, microwave antennas, and reflector antennas. Within each category, specific antenna types are described, including their basic design and purpose. Key antenna types mentioned include dipole antennas, monopole antennas, Yagi-Uda arrays, parabolic reflectors, horn antennas, and slot antennas.
A turnstile antenna, or crossed-dipole antenna,[1] is a radio antenna consisting of a set of two identical dipole antennas mounted at right angles to each other and fed in phase quadrature; the two currents applied to the dipoles are 90° out of phase.[2][3] The name reflects the notion the antenna looks like a turnstile when mounted horizontally. The antenna can be used in two possible modes. In normal mode the antenna radiates horizontally polarized radio waves perpendicular to its axis. In axial mode the antenna radiates circularly polarized radiation along its axis.
Radar and secondary radar systems use radio waves to detect objects and provide essential information to operators. Radar works by transmitting radio waves that bounce off targets and are received, allowing calculation of range and position. Secondary radar requires aircraft to carry transponders that respond to interrogations by transmitting a coded reply signal carrying additional data like identification and altitude. This improves detection range and allows transmission of emergency information.
This document discusses different types of pulsed radar systems and moving target indication techniques. It describes coherent and non-coherent radar systems, with coherent systems able to use echo phase information to determine target range and velocity. It then focuses on phase processing moving target indication using a delay-line canceller. The canceller subtracts delayed and undelayed video signals, causing signals from stationary targets to cancel out while signals from moving targets remain. This allows the radar display to only show moving targets.
Cycloconverters are used to convert AC power directly to AC power of variable magnitude and frequency. They have four main advantages over conventional AC to DC to AC conversion: they do not require an intermediate DC link, allow bidirectional power flow, can produce high quality sine waves at low frequencies without filters, and are line commutated without a separate commutation circuit. Cycloconverters are commonly used to drive large induction and synchronous motors at frequencies from 0-20Hz, such as in cement mill, ship propulsion, rolling mill, and mine applications. However, they have disadvantages of not allowing smooth stepless frequency control, producing more distortion at low frequencies, and having a more complex control circuit design.
Frequency hopping spread spectrum (FHSS) works by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. The transmitter hops from one frequency to another, transmitting short bursts of information on each channel in turn. The receiver hops in synch to receive the signals. This makes the signal resistant to interference and jamming as an eavesdropper would need to know the hop sequence to intercept the entire message coherently.
Oscillators generate an output signal without an input signal by converting DC power to AC power. They produce periodic waveforms like sine, square, triangle, and sawtooth waves. The Wien bridge oscillator is a two-stage RC coupled amplifier circuit that is stable at its resonant frequency. It uses a feedback circuit of series and parallel RC networks to produce a phase shift. Monostable multivibrators have one stable and one quasi-stable state. They switch to the quasi-stable state when triggered externally and return to the stable state after a set time period determined by resistor-capacitor values in the circuit.
The document discusses different types of antennas used for radio transmission and reception. It categorizes antennas into several groups: log periodic antennas, wire antennas, travelling wave antennas, microwave antennas, and reflector antennas. Within each category, specific antenna types are described, including their basic design and purpose. Key antenna types mentioned include dipole antennas, monopole antennas, Yagi-Uda arrays, parabolic reflectors, horn antennas, and slot antennas.
This document provides an overview of phase locked loops (PLL) including:
1. The basic components of a PLL including a phase detector, low pass filter, and voltage controlled oscillator that work together in a closed loop to lock the output frequency and phase to the input signal.
2. Examples of PLL applications such as frequency multiplication, FM demodulation, and motor speed control.
3. A more detailed description of the 565 PLL IC including its pin configuration and characteristics such as operating frequency range and drift with temperature/voltage.
Este documento presenta un resumen sobre el índice de modulación en modulación AM. Explica que el índice de modulación mide qué tanto varía la amplitud de la señal portadora debido a la señal moduladora, y que puede tomar valores entre 0 y 1. También describe cómo se calcula el índice de modulación a partir de la amplitud máxima de la señal moduladora y la amplitud de la portadora, y que depende del tamaño relativo entre esos valores. Finalmente, presenta algunos conceptos clave sobre la
This document discusses different types of choppers and cycloconverters used in DC-DC conversion. It describes the basic operation and characteristics of various classes of choppers (A, B, C, D, E) and explains step-down, step-up, and buck-boost chopper configurations. The document also covers cycloconverter types, components, waveforms, and applications. Advantages include direct AC-AC conversion in a single stage while disadvantages are their complexity and limited output frequency range.
RADAR is an electromagnetic detection system that works by transmitting electromagnetic waves and studying the echo or reflected back waves. It has applications in air traffic control, ship safety, military uses, and more. The maximum unambiguous range of a radar is determined by its pulse repetition frequency, beyond which targets will cause ambiguous echoes. MTI radar uses doppler filtering and pulse cancellation to remove stationary clutter and detect moving targets. Limitations include equipment instability, internal clutter fluctuations, and finite time observing targets while scanning. Noncoherent MTI detects moving targets using amplitude fluctuations rather than phase fluctuations as in coherent MTI radar.
This document discusses the design and applications of multicavity klystron amplifiers. It begins by explaining how multicavity klystrons are able to make use of transit time instead of fighting it. It then provides details on the design of multicavity klystrons, including how they contain multiple cavities to improve bunching and efficiency. Finally, it discusses several applications of multicavity klystron amplifiers, including use in UHF-TV transmitters, satellite communication ground stations, radar transmission, and as power oscillators.
This chapter discusses the design of IIR digital filters. It begins with preliminaries on the three steps of filter design: specifications, approximations, and implementation. It then covers characteristics of prototype analog filters, including Butterworth filters. Butterworth filters have a maximally flat magnitude response. The chapter describes designing IIR filters by first designing an analog prototype filter, then transforming it to the digital domain.
Oscillators introduction and its types, phase shift oscillators and wein bridge oscillators,difference between phase shift and wein bridge, frequency stability, oscillators principle and conditions, block diagram of oscillators, block diagram of phase shift oscillators
This document describes different types of oscillators. It discusses oscillators that use positive feedback to generate AC signals at a desired frequency. It provides block diagrams and explanations of RC phase shift oscillators, Wein bridge oscillators, Hartley oscillators, Colpitts oscillators, and Clapp oscillators. Equations for calculating the oscillation frequency of each type of oscillator are also presented.
1. The document describes experiments involving amplitude modulation, single sideband modulation, frequency modulation, and demodulation.
2. It includes the theory, block diagrams, programs, procedures and observations for experiments on AM, DSB-SC, SSB, and FM modulation and demodulation.
3. The aims are to study the processes of various modulation and demodulation techniques and calculate modulation indices by varying modulating signal parameters.
This document describes a frequency to voltage converter (FVC). It begins with an introduction to FVCs, which generate an output voltage proportional to the input signal's frequency. It then describes the basic FVC design using a differentiator, integrator, divider and square rooter. The document proposes an improved FVC using a differentiator, two RMS-DC converters and a divider to avoid spikes and calibrate for input power. It provides block diagrams and descriptions of the hardware and advantages/disadvantages of increased accuracy and operating frequency range but also potential non-linearity.
This document discusses techniques for measuring high resistance and inductance. It describes difficulties in measuring high resistance due to very small currents and leakage currents. It introduces guard circuits to eliminate errors from leakage currents. It also covers various bridges used to measure inductance through comparison, including Maxwell, capacitance comparison, and Anderson bridges. The balance equations for these bridges relate the product and sum of phase angles in the opposite arms.
Microwave devices can be passive or active. Passive devices include terminations to absorb microwave power without reflection, as well as directional couplers and phase shifters. Terminations include matched loads made of lossy materials placed in waveguides to absorb all incident power. Directional couplers are four-port devices that couple power between two connected waveguides in one direction only. Phase shifters provide a variable phase shift without changing the physical path length using materials like ferrites or dielectrics.
The document discusses different types of linear-beam microwave tubes, specifically focusing on klystron tubes. It provides details on the operation of two-cavity klystrons and reflex klystrons. Two-cavity klystrons work by velocity modulating electrons in the first cavity which become current modulated before interacting with the second cavity to produce microwave power. Reflex klystrons use a single cavity and repeller field to reflect electrons, allowing them to interact twice with the cavity field and function as an oscillator. Quantitative analyses of velocity modulation, power output, and efficiency are also presented.
The document discusses sweep frequency generators, which generate a sinusoidal output signal that is automatically varied or swept between two selectable frequencies. It describes the key components of a sweep frequency generator, including the master oscillator which produces a constant frequency signal, and a voltage controlled oscillator whose output frequency varies. The outputs of these oscillators are combined using a mixer to produce the swept frequency output signal. Sweep frequency generators are used to measure the responses of amplifiers, filters, and other electronic components over different frequency bands.
The Armstrong method is an indirect method used to generate FM by using a phase modulator. It has two parts:
1. A narrowband FM wave is generated using a phase modulator fed by a crystal oscillator. The stable oscillator allows high frequency stability.
2. Frequency multipliers and a mixer are used to increase the carrier frequency and modulation index of the narrowband FM wave to desired values for broadcast applications. This makes the Armstrong method suitable for broadcast purposes where direct methods using unstable LC oscillators cannot be used.
This chapter discusses various pulse modulation techniques including pulse amplitude modulation (PAM), pulse width modulation (PWM), pulse position modulation (PPM), and pulse code modulation (PCM). PAM varies the amplitude of pulses, PWM varies the width of pulses, PPM varies the position of pulses, and PCM converts an analog signal to a digital signal using sampling and quantization then encodes it as a binary code. Digital communication using these pulse modulation techniques offers advantages like more reliable signal reception and the ability to store, clean up, amplify, encode, and reconstruct the original signal.
Phased array antennas use interference between signals from multiple radiating elements to electronically steer antenna beams without moving parts. By adjusting the relative phases of the signals, the main beam direction can be changed. This allows for rapid electronic scanning to search for and track targets. Phased arrays are used in radar systems for military aircraft and ships where they provide advantages over mechanically scanned antennas, allowing detection of stealthy targets. Common arrangements include linear arrays that scan in one plane and planar arrays that provide two-dimensional beam steering.
This document discusses continuous wave (CW) radar and frequency modulated continuous wave (FMCW) radar. It defines radar as an electromagnetic device that can detect objects hidden from view using radio waves. Radar is classified into primary types including CW and modulated radar. CW radar uses the Doppler effect to detect moving targets based on changes in transmitted frequency. However, CW radar cannot determine range. FMCW radar modulates the transmitted frequency over time and compares the received frequency to determine both range and radial velocity of targets. Key applications of radar include military surveillance, weather monitoring, air traffic control and more.
The document summarizes key components and concepts in basic microwave engineering. It discusses waveguides and their operating frequencies based on dimensions. It also describes electric and magnetic fields in rectangular waveguides. Additional components summarized include coaxial to waveguide transitions, choke joints, coupling loops, phase shifters, junctions, tuners, mixers, isolators, circulators, directional couplers, and cavity resonators. Isolators, circulators, and directional couplers are multi-port devices that control the direction of signal propagation with differing levels of attenuation.
This document provides an overview of analog signal communication systems. It discusses how baseband signals need to be modulated to higher frequencies suitable for transmission over a channel. It introduces multiplexing as a way to send multiple signals simultaneously. It describes the main types of analog modulation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). It compares AM and FM and discusses their advantages and disadvantages. It also provides a brief overview of noise in communication systems and how it can degrade performance.
Radar is a system that uses radio waves to detect and locate distant objects. It consists of a transmitter that sends out radio waves and a receiver that collects the echoes reflected off objects. The time it takes for the echo to return can determine the distance to the object. Radar was developed during World War 2 and has both military and civilian uses such as navigation. It works by transmitting pulses of radio waves and analyzing the echoes to gather information about distant targets.
The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known.
Radar uses electromagnetic energy pulses in much the same way, as shown in Figure 1. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object.
The term RADAR is an acronym made up of the words:
RAdio (Aim) Detecting And Ranging
The term “RADAR” was officially coined as an acronym by U.S. Navy Lieutenant Commander Samuel M. Tucker and F. R. Furth in November 1940. The acronym was by agreement adopted in 1943 by the Allied powers of World War II and thereafter received general international acceptance. [1]
It refers to electronic equipment that detects the presence of objects by using reflected electromagnetic energy. Under some conditions, radar system can measure the direction, height, distance, course, and speed of these objects. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships, or other obstacles that are invisible to the naked eye because of distance, darkness, or weather.
Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions.
Basic design of radar system
The following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.
Figure 2: Block diagram of a primary radar
All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also-called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays.
Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.
This document provides an overview of phase locked loops (PLL) including:
1. The basic components of a PLL including a phase detector, low pass filter, and voltage controlled oscillator that work together in a closed loop to lock the output frequency and phase to the input signal.
2. Examples of PLL applications such as frequency multiplication, FM demodulation, and motor speed control.
3. A more detailed description of the 565 PLL IC including its pin configuration and characteristics such as operating frequency range and drift with temperature/voltage.
Este documento presenta un resumen sobre el índice de modulación en modulación AM. Explica que el índice de modulación mide qué tanto varía la amplitud de la señal portadora debido a la señal moduladora, y que puede tomar valores entre 0 y 1. También describe cómo se calcula el índice de modulación a partir de la amplitud máxima de la señal moduladora y la amplitud de la portadora, y que depende del tamaño relativo entre esos valores. Finalmente, presenta algunos conceptos clave sobre la
This document discusses different types of choppers and cycloconverters used in DC-DC conversion. It describes the basic operation and characteristics of various classes of choppers (A, B, C, D, E) and explains step-down, step-up, and buck-boost chopper configurations. The document also covers cycloconverter types, components, waveforms, and applications. Advantages include direct AC-AC conversion in a single stage while disadvantages are their complexity and limited output frequency range.
RADAR is an electromagnetic detection system that works by transmitting electromagnetic waves and studying the echo or reflected back waves. It has applications in air traffic control, ship safety, military uses, and more. The maximum unambiguous range of a radar is determined by its pulse repetition frequency, beyond which targets will cause ambiguous echoes. MTI radar uses doppler filtering and pulse cancellation to remove stationary clutter and detect moving targets. Limitations include equipment instability, internal clutter fluctuations, and finite time observing targets while scanning. Noncoherent MTI detects moving targets using amplitude fluctuations rather than phase fluctuations as in coherent MTI radar.
This document discusses the design and applications of multicavity klystron amplifiers. It begins by explaining how multicavity klystrons are able to make use of transit time instead of fighting it. It then provides details on the design of multicavity klystrons, including how they contain multiple cavities to improve bunching and efficiency. Finally, it discusses several applications of multicavity klystron amplifiers, including use in UHF-TV transmitters, satellite communication ground stations, radar transmission, and as power oscillators.
This chapter discusses the design of IIR digital filters. It begins with preliminaries on the three steps of filter design: specifications, approximations, and implementation. It then covers characteristics of prototype analog filters, including Butterworth filters. Butterworth filters have a maximally flat magnitude response. The chapter describes designing IIR filters by first designing an analog prototype filter, then transforming it to the digital domain.
Oscillators introduction and its types, phase shift oscillators and wein bridge oscillators,difference between phase shift and wein bridge, frequency stability, oscillators principle and conditions, block diagram of oscillators, block diagram of phase shift oscillators
This document describes different types of oscillators. It discusses oscillators that use positive feedback to generate AC signals at a desired frequency. It provides block diagrams and explanations of RC phase shift oscillators, Wein bridge oscillators, Hartley oscillators, Colpitts oscillators, and Clapp oscillators. Equations for calculating the oscillation frequency of each type of oscillator are also presented.
1. The document describes experiments involving amplitude modulation, single sideband modulation, frequency modulation, and demodulation.
2. It includes the theory, block diagrams, programs, procedures and observations for experiments on AM, DSB-SC, SSB, and FM modulation and demodulation.
3. The aims are to study the processes of various modulation and demodulation techniques and calculate modulation indices by varying modulating signal parameters.
This document describes a frequency to voltage converter (FVC). It begins with an introduction to FVCs, which generate an output voltage proportional to the input signal's frequency. It then describes the basic FVC design using a differentiator, integrator, divider and square rooter. The document proposes an improved FVC using a differentiator, two RMS-DC converters and a divider to avoid spikes and calibrate for input power. It provides block diagrams and descriptions of the hardware and advantages/disadvantages of increased accuracy and operating frequency range but also potential non-linearity.
This document discusses techniques for measuring high resistance and inductance. It describes difficulties in measuring high resistance due to very small currents and leakage currents. It introduces guard circuits to eliminate errors from leakage currents. It also covers various bridges used to measure inductance through comparison, including Maxwell, capacitance comparison, and Anderson bridges. The balance equations for these bridges relate the product and sum of phase angles in the opposite arms.
Microwave devices can be passive or active. Passive devices include terminations to absorb microwave power without reflection, as well as directional couplers and phase shifters. Terminations include matched loads made of lossy materials placed in waveguides to absorb all incident power. Directional couplers are four-port devices that couple power between two connected waveguides in one direction only. Phase shifters provide a variable phase shift without changing the physical path length using materials like ferrites or dielectrics.
The document discusses different types of linear-beam microwave tubes, specifically focusing on klystron tubes. It provides details on the operation of two-cavity klystrons and reflex klystrons. Two-cavity klystrons work by velocity modulating electrons in the first cavity which become current modulated before interacting with the second cavity to produce microwave power. Reflex klystrons use a single cavity and repeller field to reflect electrons, allowing them to interact twice with the cavity field and function as an oscillator. Quantitative analyses of velocity modulation, power output, and efficiency are also presented.
The document discusses sweep frequency generators, which generate a sinusoidal output signal that is automatically varied or swept between two selectable frequencies. It describes the key components of a sweep frequency generator, including the master oscillator which produces a constant frequency signal, and a voltage controlled oscillator whose output frequency varies. The outputs of these oscillators are combined using a mixer to produce the swept frequency output signal. Sweep frequency generators are used to measure the responses of amplifiers, filters, and other electronic components over different frequency bands.
The Armstrong method is an indirect method used to generate FM by using a phase modulator. It has two parts:
1. A narrowband FM wave is generated using a phase modulator fed by a crystal oscillator. The stable oscillator allows high frequency stability.
2. Frequency multipliers and a mixer are used to increase the carrier frequency and modulation index of the narrowband FM wave to desired values for broadcast applications. This makes the Armstrong method suitable for broadcast purposes where direct methods using unstable LC oscillators cannot be used.
This chapter discusses various pulse modulation techniques including pulse amplitude modulation (PAM), pulse width modulation (PWM), pulse position modulation (PPM), and pulse code modulation (PCM). PAM varies the amplitude of pulses, PWM varies the width of pulses, PPM varies the position of pulses, and PCM converts an analog signal to a digital signal using sampling and quantization then encodes it as a binary code. Digital communication using these pulse modulation techniques offers advantages like more reliable signal reception and the ability to store, clean up, amplify, encode, and reconstruct the original signal.
Phased array antennas use interference between signals from multiple radiating elements to electronically steer antenna beams without moving parts. By adjusting the relative phases of the signals, the main beam direction can be changed. This allows for rapid electronic scanning to search for and track targets. Phased arrays are used in radar systems for military aircraft and ships where they provide advantages over mechanically scanned antennas, allowing detection of stealthy targets. Common arrangements include linear arrays that scan in one plane and planar arrays that provide two-dimensional beam steering.
This document discusses continuous wave (CW) radar and frequency modulated continuous wave (FMCW) radar. It defines radar as an electromagnetic device that can detect objects hidden from view using radio waves. Radar is classified into primary types including CW and modulated radar. CW radar uses the Doppler effect to detect moving targets based on changes in transmitted frequency. However, CW radar cannot determine range. FMCW radar modulates the transmitted frequency over time and compares the received frequency to determine both range and radial velocity of targets. Key applications of radar include military surveillance, weather monitoring, air traffic control and more.
The document summarizes key components and concepts in basic microwave engineering. It discusses waveguides and their operating frequencies based on dimensions. It also describes electric and magnetic fields in rectangular waveguides. Additional components summarized include coaxial to waveguide transitions, choke joints, coupling loops, phase shifters, junctions, tuners, mixers, isolators, circulators, directional couplers, and cavity resonators. Isolators, circulators, and directional couplers are multi-port devices that control the direction of signal propagation with differing levels of attenuation.
This document provides an overview of analog signal communication systems. It discusses how baseband signals need to be modulated to higher frequencies suitable for transmission over a channel. It introduces multiplexing as a way to send multiple signals simultaneously. It describes the main types of analog modulation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). It compares AM and FM and discusses their advantages and disadvantages. It also provides a brief overview of noise in communication systems and how it can degrade performance.
Radar is a system that uses radio waves to detect and locate distant objects. It consists of a transmitter that sends out radio waves and a receiver that collects the echoes reflected off objects. The time it takes for the echo to return can determine the distance to the object. Radar was developed during World War 2 and has both military and civilian uses such as navigation. It works by transmitting pulses of radio waves and analyzing the echoes to gather information about distant targets.
The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known.
Radar uses electromagnetic energy pulses in much the same way, as shown in Figure 1. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object.
The term RADAR is an acronym made up of the words:
RAdio (Aim) Detecting And Ranging
The term “RADAR” was officially coined as an acronym by U.S. Navy Lieutenant Commander Samuel M. Tucker and F. R. Furth in November 1940. The acronym was by agreement adopted in 1943 by the Allied powers of World War II and thereafter received general international acceptance. [1]
It refers to electronic equipment that detects the presence of objects by using reflected electromagnetic energy. Under some conditions, radar system can measure the direction, height, distance, course, and speed of these objects. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships, or other obstacles that are invisible to the naked eye because of distance, darkness, or weather.
Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions.
Basic design of radar system
The following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.
Figure 2: Block diagram of a primary radar
All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also-called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays.
Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.
Airport servilanc radar system Asr 8 usful presentationFaraidonSafi
1. The ASR-8 is an airport surveillance radar system with dual channels that allows air traffic controllers to monitor aircraft within 60 nautical miles.
2. It uses components like a diplexer, circulator, and dummy load to switch transmitter power to the antenna and receive returning signals while protecting the receiver.
3. Maintenance can be performed on one channel while the other remains operational, and components like the diplexer and waveguide switches allow both channels to operate simultaneously in a frequency diversity mode for improved detection.
This document provides an overview of radar systems used for fire control and describes their main components. It discusses how radar works by transmitting radio waves and detecting their reflection off objects. Fire control radars emit narrow beams to accurately track targets and guide weapons. They are part of larger fire control systems along with gun data computers and directors to assist weapon systems in hitting targets faster and more precisely. The majority of the work involves radar systems that control the direction and firing of guns and missiles.
The document discusses different types of radar systems and their components and principles of operation. It covers topics like pulse radar vs continuous wave radar, components of each type of system like transmitter, receiver, antennas, and how factors like pulse width, repetition frequency and power affect radar performance and capabilities. It also discusses modulation techniques, antenna beam formation, and different types of radar displays.
Radar uses radio waves to detect distant objects by transmitting pulses and receiving echoes. Marine radars are used onboard ships and have several key components: a power supply, modulator, transmitter, antenna/scanner assembly, receiver, and display screen. The radar transmits pulses that travel at the speed of light and bounce off targets, with the echoes received by the antenna and displayed on the screen. Factors like pulse length, receiver gain, target size/movement, and environmental conditions can affect the radar's ability to resolve targets in range and bearing.
This document provides an overview of two basic radar types: pulse transmission radar and continuous wave radar. It describes the key components and operating principles of each. Pulse radar relies on pulse width and repetition frequency to determine range, while continuous wave radar uses the Doppler effect of the frequency shift in returned echoes to deduce information about targets. The document also discusses radar modulation techniques, antenna design and beamforming, and other major components like transmitters, receivers, and waveguides.
Design of Rugged High Voltage Power Supplies for use in Low Noise Multi-mode Radar Transmitter Sub-Systems.
This paper covers an approach to the design of High Voltage Power Supply Units for operating Travelling Wave Tube Amplifiers in Pulse Doppler Radar Transmitter Sub‐Systems where ultra low noise RF Output is mandatory.
This document outlines a unit plan on radar communication. It includes sections on radar principles and applications, radar frequency bands, pulse-related terms, the radar range equation, duplexer and display systems, types of radar including pulse, CW, FMCW, MTI and secondary radar, landing systems including ILS and GCA, and an introduction to SONAR. Various radar concepts are defined and block diagrams of radar systems are provided with explanations. The unit plan allocates 1 hour for each sub-section and includes learning objectives.
This document provides an overview of radar systems. It discusses what radar is, the evolution of radar from its initial uses detecting objects with radio waves in the late 1800s. It then explains the basic principles of how radar works to detect objects using radio signal transmission and reflection. Key components of radar systems like transmitters, receivers, antennas and signal processing are described. Applications of radar systems include military, remote sensing, air traffic control, and navigation. The document also discusses radar modulators and antenna design considerations for radar.
The document provides an overview of radar principles and systems. It describes the basic operation and components of pulse radar and continuous wave radar. Key factors that affect radar performance are discussed, including signal reception, receiver bandwidth, pulse shape, power relationship, beam width, pulse repetition frequency, antenna gain, radar cross section of targets, and more. The roles of various components in pulse and continuous wave radar systems are outlined. Modulation techniques, antenna types, and other topics are also covered at a high level.
This document provides an overview of radar principles and systems. It describes the basic operation of pulse radar and continuous wave radar. Key components of pulse radar systems are discussed, including synchronizers, transmitters, antennas, duplexers, receivers, and display units. Factors that influence radar performance such as signal reception, receiver bandwidth, pulse shape, and power are also covered. Different modulation techniques and specific radar types like frequency modulated CW radar and pulse Doppler radar are described.
A low-level AM transmitter performs amplitude modulation early in the transmitter circuit, near the oscillator and buffer amplifier stages, where power levels are low. A high-level AM transmitter performs amplitude modulation in the final power amplifier stage, where higher power levels allow for greater transmission efficiency but limit the modulation to AM. Both approaches have advantages - low-level transmitters can produce different modulation types but are less efficient, while high-level transmitters are more efficient but restricted to AM modulation. The document discusses the components, signal paths, and operation of both low-level and high-level AM transmitter circuits.
The document discusses adaptive moving target indication (MTI) radar. It describes how MTI radar uses the Doppler effect to discriminate moving targets from stationary clutter. Adaptive filters can be used for MTI to adjust to spatially and temporally varying clutter environments. The objective of the project is to design an adaptive MTI filter with improved performance in non-stationary clutter environments. This will involve estimating pulse-to-pulse amplitude variations of the clutter process and implementing this estimator in the adaptive MTI filter to help it adapt to non-stationary clutter behavior. Results applying this adaptive MTI filter to real radar data show extensive reduction in clutter detections in the radar image.
There are two basic types of radar: pulse transmission radar and continuous wave radar. Pulse transmission radar uses pulses of radio waves and measures the echo to determine characteristics like range, velocity, and direction of targets. Continuous wave radar transmits a continuous radio signal and detects frequency changes in the return echo to deduce such properties. The performance of radars is influenced by various factors related to the pulse shape, width, repetition frequency, power, and the receiver's bandwidth, sensitivity, and signal-to-noise ratio. Trade-offs exist between different performance characteristics like range accuracy, maximum range, and resolution.
The document discusses the basic principles and components of pulse transmission and continuous wave radar systems. It describes how pulse radar determines range using pulse width, pulse repetition frequency, and time of return signals. Key components of pulse radar systems are identified as the synchronizer, transmitter, antenna, duplexer, receiver and display unit. Continuous wave radar relies on Doppler frequency shifts from moving targets and uses separate transmit and receive antennas. Modulation techniques for radar waves include amplitude, frequency, pulse-amplitude and pulse-frequency modulation. Factors that affect radar performance such as signal reception, bandwidth, power, beamwidth and signal-to-noise ratio are also covered.
Radar uses electromagnetic pulses and antennas to detect objects at a distance. It works by transmitting pulses that reflect off objects and return to the radar receiver. This allows radar to determine characteristics of detected objects like range, velocity, and bearing. The key components of a radar system are the transmitter, receiver, power supply, synchronizer, duplexer, antenna, and display. The radar equation relates system parameters like transmitted power, antenna gain, target radar cross section, and wavelength to the maximum detectable range. Common pulse parameters include pulse width, repetition time and frequency, and duty cycle. Bearing is the angular position of a target measured in the horizontal or vertical plane.
This technical report discusses the components and system design of radar systems. It describes some key subsystems including antennas, duplexers, and the radio frequency subsystem. It also discusses digital waveform generators and frequency synthesizers/oscillators. Antennas are the interface between the radar system and free space, transmitting energy in beams and collecting echo signals. Duplexers use circulators to switch the radar between transmit and receive modes. The radio frequency subsystem includes antennas, duplexers, and filters to transmit signals and filter received signals. Digital waveform generators store and output signals using digital memories and D/A converters. Frequency synthesizers and oscillators generate the radio frequencies used.
Power supplies convert alternating current (AC) to direct current (DC) using components like transformers, rectifiers, and filters. Common rectifier types include half-wave, full-wave center-tapped, and full-wave bridge rectifiers. Filters use inductors and capacitors to smooth the pulsating DC output into a steady DC voltage. Safety is important when working with power supplies, as filter capacitors can hold a charge even after power is turned off. Switching power supplies are more efficient than linear supplies and are commonly used in electronics today.
Subsystems of radar and signal processing Ronak Vyas
This document discusses subsystems of radar and signal processing, specifically focusing on ST (Stratosphere Troposphere) radar. It begins by introducing the goals of understanding basic radar concepts and studying ST radar. It then provides an overview of key radar subsystems including antennas, duplexers, transmitters, and receivers. The document concludes by describing common signal processing techniques used in radar like correlation, Doppler filtering, and detection processing.
The Department of Veteran Affairs (VA) invited Taylor Paschal, Knowledge & Information Management Consultant at Enterprise Knowledge, to speak at a Knowledge Management Lunch and Learn hosted on June 12, 2024. All Office of Administration staff were invited to attend and received professional development credit for participating in the voluntary event.
The objectives of the Lunch and Learn presentation were to:
- Review what KM ‘is’ and ‘isn’t’
- Understand the value of KM and the benefits of engaging
- Define and reflect on your “what’s in it for me?”
- Share actionable ways you can participate in Knowledge - - Capture & Transfer
Dandelion Hashtable: beyond billion requests per second on a commodity serverAntonios Katsarakis
This slide deck presents DLHT, a concurrent in-memory hashtable. Despite efforts to optimize hashtables, that go as far as sacrificing core functionality, state-of-the-art designs still incur multiple memory accesses per request and block request processing in three cases. First, most hashtables block while waiting for data to be retrieved from memory. Second, open-addressing designs, which represent the current state-of-the-art, either cannot free index slots on deletes or must block all requests to do so. Third, index resizes block every request until all objects are copied to the new index. Defying folklore wisdom, DLHT forgoes open-addressing and adopts a fully-featured and memory-aware closed-addressing design based on bounded cache-line-chaining. This design offers lock-free index operations and deletes that free slots instantly, (2) completes most requests with a single memory access, (3) utilizes software prefetching to hide memory latencies, and (4) employs a novel non-blocking and parallel resizing. In a commodity server and a memory-resident workload, DLHT surpasses 1.6B requests per second and provides 3.5x (12x) the throughput of the state-of-the-art closed-addressing (open-addressing) resizable hashtable on Gets (Deletes).
LF Energy Webinar: Carbon Data Specifications: Mechanisms to Improve Data Acc...DanBrown980551
This LF Energy webinar took place June 20, 2024. It featured:
-Alex Thornton, LF Energy
-Hallie Cramer, Google
-Daniel Roesler, UtilityAPI
-Henry Richardson, WattTime
In response to the urgency and scale required to effectively address climate change, open source solutions offer significant potential for driving innovation and progress. Currently, there is a growing demand for standardization and interoperability in energy data and modeling. Open source standards and specifications within the energy sector can also alleviate challenges associated with data fragmentation, transparency, and accessibility. At the same time, it is crucial to consider privacy and security concerns throughout the development of open source platforms.
This webinar will delve into the motivations behind establishing LF Energy’s Carbon Data Specification Consortium. It will provide an overview of the draft specifications and the ongoing progress made by the respective working groups.
Three primary specifications will be discussed:
-Discovery and client registration, emphasizing transparent processes and secure and private access
-Customer data, centering around customer tariffs, bills, energy usage, and full consumption disclosure
-Power systems data, focusing on grid data, inclusive of transmission and distribution networks, generation, intergrid power flows, and market settlement data
zkStudyClub - LatticeFold: A Lattice-based Folding Scheme and its Application...Alex Pruden
Folding is a recent technique for building efficient recursive SNARKs. Several elegant folding protocols have been proposed, such as Nova, Supernova, Hypernova, Protostar, and others. However, all of them rely on an additively homomorphic commitment scheme based on discrete log, and are therefore not post-quantum secure. In this work we present LatticeFold, the first lattice-based folding protocol based on the Module SIS problem. This folding protocol naturally leads to an efficient recursive lattice-based SNARK and an efficient PCD scheme. LatticeFold supports folding low-degree relations, such as R1CS, as well as high-degree relations, such as CCS. The key challenge is to construct a secure folding protocol that works with the Ajtai commitment scheme. The difficulty, is ensuring that extracted witnesses are low norm through many rounds of folding. We present a novel technique using the sumcheck protocol to ensure that extracted witnesses are always low norm no matter how many rounds of folding are used. Our evaluation of the final proof system suggests that it is as performant as Hypernova, while providing post-quantum security.
Paper Link: https://eprint.iacr.org/2024/257
"Choosing proper type of scaling", Olena SyrotaFwdays
Imagine an IoT processing system that is already quite mature and production-ready and for which client coverage is growing and scaling and performance aspects are life and death questions. The system has Redis, MongoDB, and stream processing based on ksqldb. In this talk, firstly, we will analyze scaling approaches and then select the proper ones for our system.
Northern Engraving | Nameplate Manufacturing Process - 2024Northern Engraving
Manufacturing custom quality metal nameplates and badges involves several standard operations. Processes include sheet prep, lithography, screening, coating, punch press and inspection. All decoration is completed in the flat sheet with adhesive and tooling operations following. The possibilities for creating unique durable nameplates are endless. How will you create your brand identity? We can help!
5th LF Energy Power Grid Model Meet-up SlidesDanBrown980551
5th Power Grid Model Meet-up
It is with great pleasure that we extend to you an invitation to the 5th Power Grid Model Meet-up, scheduled for 6th June 2024. This event will adopt a hybrid format, allowing participants to join us either through an online Mircosoft Teams session or in person at TU/e located at Den Dolech 2, Eindhoven, Netherlands. The meet-up will be hosted by Eindhoven University of Technology (TU/e), a research university specializing in engineering science & technology.
Power Grid Model
The global energy transition is placing new and unprecedented demands on Distribution System Operators (DSOs). Alongside upgrades to grid capacity, processes such as digitization, capacity optimization, and congestion management are becoming vital for delivering reliable services.
Power Grid Model is an open source project from Linux Foundation Energy and provides a calculation engine that is increasingly essential for DSOs. It offers a standards-based foundation enabling real-time power systems analysis, simulations of electrical power grids, and sophisticated what-if analysis. In addition, it enables in-depth studies and analysis of the electrical power grid’s behavior and performance. This comprehensive model incorporates essential factors such as power generation capacity, electrical losses, voltage levels, power flows, and system stability.
Power Grid Model is currently being applied in a wide variety of use cases, including grid planning, expansion, reliability, and congestion studies. It can also help in analyzing the impact of renewable energy integration, assessing the effects of disturbances or faults, and developing strategies for grid control and optimization.
What to expect
For the upcoming meetup we are organizing, we have an exciting lineup of activities planned:
-Insightful presentations covering two practical applications of the Power Grid Model.
-An update on the latest advancements in Power Grid -Model technology during the first and second quarters of 2024.
-An interactive brainstorming session to discuss and propose new feature requests.
-An opportunity to connect with fellow Power Grid Model enthusiasts and users.
"Frontline Battles with DDoS: Best practices and Lessons Learned", Igor IvaniukFwdays
At this talk we will discuss DDoS protection tools and best practices, discuss network architectures and what AWS has to offer. Also, we will look into one of the largest DDoS attacks on Ukrainian infrastructure that happened in February 2022. We'll see, what techniques helped to keep the web resources available for Ukrainians and how AWS improved DDoS protection for all customers based on Ukraine experience
Must Know Postgres Extension for DBA and Developer during MigrationMydbops
Mydbops Opensource Database Meetup 16
Topic: Must-Know PostgreSQL Extensions for Developers and DBAs During Migration
Speaker: Deepak Mahto, Founder of DataCloudGaze Consulting
Date & Time: 8th June | 10 AM - 1 PM IST
Venue: Bangalore International Centre, Bangalore
Abstract: Discover how PostgreSQL extensions can be your secret weapon! This talk explores how key extensions enhance database capabilities and streamline the migration process for users moving from other relational databases like Oracle.
Key Takeaways:
* Learn about crucial extensions like oracle_fdw, pgtt, and pg_audit that ease migration complexities.
* Gain valuable strategies for implementing these extensions in PostgreSQL to achieve license freedom.
* Discover how these key extensions can empower both developers and DBAs during the migration process.
* Don't miss this chance to gain practical knowledge from an industry expert and stay updated on the latest open-source database trends.
Mydbops Managed Services specializes in taking the pain out of database management while optimizing performance. Since 2015, we have been providing top-notch support and assistance for the top three open-source databases: MySQL, MongoDB, and PostgreSQL.
Our team offers a wide range of services, including assistance, support, consulting, 24/7 operations, and expertise in all relevant technologies. We help organizations improve their database's performance, scalability, efficiency, and availability.
Contact us: info@mydbops.com
Visit: https://www.mydbops.com/
Follow us on LinkedIn: https://in.linkedin.com/company/mydbops
For more details and updates, please follow up the below links.
Meetup Page : https://www.meetup.com/mydbops-databa...
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Blogs: https://www.mydbops.com/blog/
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How to Interpret Trends in the Kalyan Rajdhani Mix Chart.pdfChart Kalyan
A Mix Chart displays historical data of numbers in a graphical or tabular form. The Kalyan Rajdhani Mix Chart specifically shows the results of a sequence of numbers over different periods.
Taking AI to the Next Level in Manufacturing.pdfssuserfac0301
Read Taking AI to the Next Level in Manufacturing to gain insights on AI adoption in the manufacturing industry, such as:
1. How quickly AI is being implemented in manufacturing.
2. Which barriers stand in the way of AI adoption.
3. How data quality and governance form the backbone of AI.
4. Organizational processes and structures that may inhibit effective AI adoption.
6. Ideas and approaches to help build your organization's AI strategy.
Conversational agents, or chatbots, are increasingly used to access all sorts of services using natural language. While open-domain chatbots - like ChatGPT - can converse on any topic, task-oriented chatbots - the focus of this paper - are designed for specific tasks, like booking a flight, obtaining customer support, or setting an appointment. Like any other software, task-oriented chatbots need to be properly tested, usually by defining and executing test scenarios (i.e., sequences of user-chatbot interactions). However, there is currently a lack of methods to quantify the completeness and strength of such test scenarios, which can lead to low-quality tests, and hence to buggy chatbots.
To fill this gap, we propose adapting mutation testing (MuT) for task-oriented chatbots. To this end, we introduce a set of mutation operators that emulate faults in chatbot designs, an architecture that enables MuT on chatbots built using heterogeneous technologies, and a practical realisation as an Eclipse plugin. Moreover, we evaluate the applicability, effectiveness and efficiency of our approach on open-source chatbots, with promising results.
AppSec PNW: Android and iOS Application Security with MobSFAjin Abraham
Mobile Security Framework - MobSF is a free and open source automated mobile application security testing environment designed to help security engineers, researchers, developers, and penetration testers to identify security vulnerabilities, malicious behaviours and privacy concerns in mobile applications using static and dynamic analysis. It supports all the popular mobile application binaries and source code formats built for Android and iOS devices. In addition to automated security assessment, it also offers an interactive testing environment to build and execute scenario based test/fuzz cases against the application.
This talk covers:
Using MobSF for static analysis of mobile applications.
Interactive dynamic security assessment of Android and iOS applications.
Solving Mobile app CTF challenges.
Reverse engineering and runtime analysis of Mobile malware.
How to shift left and integrate MobSF/mobsfscan SAST and DAST in your build pipeline.
The Microsoft 365 Migration Tutorial For Beginner.pptxoperationspcvita
This presentation will help you understand the power of Microsoft 365. However, we have mentioned every productivity app included in Office 365. Additionally, we have suggested the migration situation related to Office 365 and how we can help you.
You can also read: https://www.systoolsgroup.com/updates/office-365-tenant-to-tenant-migration-step-by-step-complete-guide/
1. „Radartutorial“ (www.radartutorial.eu)
Radartutorial
Book 4 “Radar Transmitter”
This educational endowment is a printable summary of the fourth chapter of the internet
representation “Radar Basics” on www.radartutorial.eu , containing a lecture on the principles of
radar technology.
Table of Contents
Radartutorial..................................................................................................................................1
Table of Contents...................................................................................................................1
Learning 0bjectives:...............................................................................................................1
Radar Transmitter......................................................................................................................2
Tasks of a radar transmitter....................................................................................................2
Division of radar transmitters..................................................................................................2
High-Power Oscillator as Transmitter.................................................................................2
High-Power Amplifier as Transmitter..................................................................................2
The Concept of “Coherence” .............................................................................................3
Non-coherent Radar Processing........................................................................................3
Coherent Radar Processing...............................................................................................3
Pseudo-coherent Radar ........................................................................................................4
Disadvantages of the pseudo-coherent radar.........................................................................6
Modulator ..........................................................................................................................6
Thyratron ...............................................................................................................................8
Fully Coherent Radar ............................................................................................................9
Solid State Transmitter ........................................................................................................10
Powermodules.....................................................................................................................10
Waveform-Generator .......................................................................................................10
Pulse Compression .............................................................................................................13
Pulse compression with linear FM waveform........................................................................14
SAW- Devices .................................................................................................................14
Time-Side-Lobes..................................................................................................................16
Pulse compression with non-linear FM waveform................................................................16
Learning 0bjectives:
This chapter describes the different types of transmitters used in radar sets. Upon completion of
this chapter you will be able to:
• Describe the general task of and know the demands on a radar transmitter,
• State the meaning of the term “Coherence”
• Describe the general design of a fully-coherent radar transmitter and compare it with the
general design of a pseudo-coherent radar transmitter.
• Describe the technology of Intra-pulse Modulation and the Pulse Compression.
• State the different methods of Intra-pulse Modulation.
1
2. Figure 1: self-oscillating Transmitter using a
Magnetron (ATC radar ASR-910)
„Radartutorial“ (www.radartutorial.eu)
Radar Transmitter
Tasks of a radar transmitter
The radar transmitter produces the short duration high-power RF pulses of energy that are
radiated into space by the antenna. The radar transmitter is required to have the following
technical and operating characteristics:
The transmitter must have the ability to generate the required mean RF power and the required
peak power
• The transmitter must have a suitable RF bandwidth.
• The transmitter must have a high RF stability to meet signal processing requirements
• The transmitter must be easily modulated to meet waveform design requirements.
• The transmitter must be efficient, reliable and easy to maintain and the life expectancy
and cost of the output device must be acceptable.
The radar transmitter is designed around the selected
output device and most of the transmitter chapter is
devoted to describing output devices therefore.
Division of radar transmitters
High-Power Oscillator as Transmitter
One main type of transmitters is the keyed-oscillator type.
In this transmitter one stage or tube, usually a magnetron
produces the RF pulse. The oscillator tube is keyed by a
high-power dc pulse of energy generated by a separate
unit called the modulator. This transmitting system is called
POT (Power Oscillator Transmitter). Radar units fitted with
a POT are either non-coherent or pseudo-coherent.
High-Power Amplifier as Transmitter
Power-Amplifier-Transmitters (PAT) is used in many recently developed radar sets. In this
system the transmitting pulse is caused with a small performance in a waveform generator. It is
taken to the necessary power with an amplifier following (Amplitron, Klystron or Solid-State-
Amplifier). Radar units fitted with a PAT are fully coherent in the majority of cases.
A special case of the PAT is the active antenna.
• Even every antenna element
• or every antenna-group
is equipped with an own amplifier here.
Solid-state transmit/receive modules appear attractive for constructing phased array radar
systems. However, microwave tube technology1
continues to offer substantial advantages in
power output over solid-state technology.
1
Microwave velocity modulated tubes are described in book 5.
2
3. Figure 2: non-coherent radar processing: every pulse
starts with a random phase
Figure 3: coherent radar processing: every pulse starts
with the same phase
„Radartutorial“ (www.radartutorial.eu)
The Concept of “Coherence”
Whether a radar set is coherent or non-coherent always depend on the transmitter. As a
transmitter different systems are used in radar.
Non-coherent Radar Processing
One of the transmitting systems is the POT (Power
Oscillator Transmitter) which is self oscillating. When
such a device is switched on and off as a result of
modulation by the rectangular modulating pulse, the
starting phase of each pulse is not the same for the
different successive pulses. The starting phase is a
random function related to the start up process of
the oscillator.
Note: Self oscillating transmitter gives random
phase pulse to pulse and is not coherent!
Coherent Radar Processing
Another transmitter-system is the PAT (Power-
Amplifier-Transmitter). In this case, the high-power
amplifier is driven by a highly stable continuous RF
source, called the waveform generator. Modulating
the output stage in response to the PRF does not
affect the phase of the driver/RF source. Assuming
the RF is a multiple of the PRF (as is normally the
case), each pulse starts with the same phase.
Systems, which inherently maintain a high level of
phase coherence from pulse to pulse, are termed
fully coherent. Note that phase coherence is
maintained even if the PRF and RF are not locked
together (provided the RF source is phase stable).
As stated, it is common practice to lock the PRF to
the RF phase and this assumption makes it easier to
understand the concept of coherence.
Note: Low Power oscillator and amplifier give same phase pulse to pulse and are a
coherent system!
The most important benefit of this system is the ability to differentiate relatively small differences
in velocity (which correspond to small differences in phase). This coherent target processing
offers Doppler resolution/estimation and provides less interference and signal/noise benefits
relative to non-coherent processing.
3
4. „Radartutorial“ (www.radartutorial.eu)
Pseudo-coherent Radar
A requirement for any Doppler radar is coherence; that is, some definite phase relationship must
exist between the transmitted frequency and the reference frequency, which is used to detect the
Doppler shift of the receiver signal. Moving objects are detected by the phase difference between
the target signal and background clutter and noise components. Phase detection of this type
relies on coherence between the transmitter frequency and the receiver reference frequency.
If the transmitter output stage is a self oscillating device, the pulse to pulse phase is random on
transmission. In coherent detection, a stable CW reference oscillator signal, which is locked in
phase with the transmitter during each transmitted pulse, is mixed with the echo signal to produce
a beat or difference signal. Since the reference oscillator and the transmitter are locked in phase,
the echoes are effectively compared with the transmitter in frequency and phase. This phase
reference must be maintained from the transmitted pulse to the return pulse picked up by the
receiver. Pseudo-coherent Radar sets are sometimes called: „coherent-on-receive”.
Figure 4: The principle of a pseudo-coherent radar.
Synchronizer The synchronizer supplies the synchronizing signals that time the transmitted pulses, the
indicator, and other associated circuits.
Modulator The oscillator tube of the transmitter is keyed by a high-power dc pulse of energy
generated by this separate unit called the modulator.
Tx-Tube The Tx-Tube is a self-oscillating tube generating high-power microwaves.
Duplexer The duplexer alternately switches the antenna between the transmitter and receiver so that
only one antenna need be used. This switching is necessary because the high-power
pulses of the transmitter would destroy the receiver if energy were allowed to enter the
receiver.
Antenna The Antenna transfers the transmitter energy to signals in space with the required distribution and
efficiency. This process is applied in an identical way on reception.
Mixer stage The function of the mixer stage is to convert the received rf energy to a lower, intermediate
frequency (IF) that is easier to amplify and manipulate electronically. The intermediate
frequency is usually 30 op to 74 megahertz. It is obtained by heterodyning the received
signal with a local-oscillator signal in the mixer stage. The mixer stage converts the
received signal to the lower IF signal without distorting the data on the received signal.
4
5. „Radartutorial“ (www.radartutorial.eu)
IF-Amplifier After conversion to the intermediate frequency, the signal is amplified in several IF-
amplifier stages. Most of the gain of the receiver is developed in the IF-amplifier stages.
The overall bandwidth of the receiver is often determined by the bandwidth of the IF-
stages.
Mixer stage
2
The directional coupler provides a sample of the transmitter output on every pulse. This
signal adjusts the STALO frequency via the AFC but more importantly, it adjusts the phase
of the COHO, locking it to the phase reference from the non-coherent transmitter.
Automatic
Frequency
Control
(AFC)
As in all superheterodyne receivers, controlling the frequency of the local oscillator keeps the
receiver tuned. Since this tuning is critical, some form of automatic frequency control (afc) is
essential to avoid constant manual tuning. Automatic frequency control circuits mix an attenuated
portion of the transmitted signal with the local oscillator signal to form an IF signal. This signal is
applied to a frequency-sensitive discriminator that produces an output voltage proportional in
amplitude and polarity to any change in IF-frequency. If the IF signal is at the discriminator center
frequency, no discriminator output occurs. The center frequency of the discriminator is essentially
a reference frequency for the IF-signal.
The output of the discriminator provides a control voltage to maintain the local oscillator at the
correct frequency.
Stable Local
Oscillator
(StaLO)
As the receiver is normally a super heterodyne, a stable local oscillator known as the StaLO down
converts the signal to intermediate frequency.
Most radar receivers use a 30 up to 74 megahertz intermediate frequency. The IF is produced by
mixing a local oscillator signal with the incoming signal. The local oscillator is, therefore, essential
to efficient operation and must be both tunable and very stable. For example, if the local oscillator
frequency is 3,000 megahertz, a frequency change of 0.1 percent will produce a frequency shift of
3 megahertz. This is equal to the bandwidth of most receivers and would greatly decrease
receiver gain.
The power output requirement for most local oscillators is small (20 to 50 milliwatts) because
most receivers use crystal mixers that require very little power.
The local oscillator output frequency must be tunable over a range of several megahertz in the
4,000-megahertz region. The local oscillator must compensate for any changes in the transmitted
frequency and maintain a constant 30 up to 74 megahertz difference between the oscillator and
the transmitter frequency. A local oscillator that can be tuned by varying the applied voltage is
most desirable.
Phase-
sensitive
detector
The IF-signal is passed to a phase sensitive detector (PSD) which converts the signal to base
band, while faithfully retaining the full phase and quadrature information of the Doppler signal.
This means, the phase-sensitive detector produces a video signal. The amplitude of the video
signal is determined by the phase difference between the COHO reference signal and the IF echo
signals. This phase difference is the same as that between the actual transmitted pulse and its
echo. The resultant video signal may be either positive or negative.
Signal
processor
The signal processor is that part of the system which separates targets from clutter on the basis
of Doppler content and amplitude characteristics.
Directional
Coupler
The directional coupler provides a sample of the transmitter output on every pulse. This signal
adjusts the STALO frequency via the AFC but more importantly, it adjusts the phase of the
COHO, locking it to the phase reference from the non-coherent transmitter (e.g. Magnetron). The
phase synchronization of the COHO by means of a sample of the magnetron output is mandatory
because there is no phase correlation between two successive RF pulses of the magnetron.
Coherent
oscillator
The Coherent Oscillator (COHO) provides a low-power continuous RF-energy. It enables the
down conversion process into the phase sensitive detector, whilst maintaining an accurate phase
reference. The COHO lock pulse is originated by the transmitted pulse. It is used to synchronize
the COHO to a fixed phase relationship with the transmitted frequency at each transmitted pulse.
The COHO takes over the phase of the transmitter tube and provides it to the receiver part of the
system. This is the reason why the pseudo-coherent radar is also called “coherent on receive”.
Indicator The indicator should present to the observer a continuous, easily understandable, graphic picture
of the relative position of radar targets.
5
6. Figure 6: ancient modulator (Spoon Rest D)
showing all components of a modulatorFigure 5: Thyratron Modulator
„Radartutorial“ (www.radartutorial.eu)
Disadvantages of the pseudo-coherent radar
The pseudo-coherent radar is a retired one today, but some older (or low-cost) radar sets are still
operational. The disadvantages of the pseudo-coherent radar can be summarized as follows:
• The phase locking process is not as accurate as a fully coherent system, which reduces
the MTI Improvement factor.
• This technique cannot be applied to frequency agile radar. Frequency change in a
magnetron relies on the mechanical tuning of a cavity and it is essentially a narrow band
device.
• It is not flexible and cannot easily accommodate changes in the PRF, pulsewidth or other
parameters of the transmitted signal. Such changes are straightforward in fully coherent
radar because they can be performed at low level. It is also impossible to perform FM
modulation (which is mandatory for a pulse compression radar) with this type of system.
• Second times around echoes are returns from large fixed clutter areas located a long
distance from the radar. Because they originate from a large distance, such echoes are
returned after a second magnetron pulse has been transmitted. However, they pertain to
the first pulse transmitted by the magnetron. Such echoes are range ambiguous but, in
addition, second time around clutter will not cancel. This is due to the fact that the phase
locking of the COHO applies only to the last transmitted pulse.
Modulator
Radio frequency energy in radar is transmitted in short pulses with time durations that may vary
from 1 to 50 microseconds or more. A keyed oscillator transmitter needs a special modulator.
This modulator produces impulses of high voltage switching the microwave tube on/off.
The hydrogen thyratron modulator is the most common radar modulator. It employs a pulse-
forming network that is charged up slowly to a high value of voltage. The network is discharged
rapidly through a pulse transformer by the thyratron keyed tube to develop an output pulse; the
shape and duration of the pulse are determined by the electrical characteristics of the pulse-
forming network and of the pulse transformer.
As circuit for storing energy the thyratron modulator uses essentially a short section of artificial
transmission line which is known as the pulse- forming network (PFN). Via the charging path this
PFN is charged on the double voltage of the high voltage power supply with help of the magnetic
field of the charging impedance. Simultaneously this charging impedance limits the charging
current. The charging diode prevents that the PFN discharge him about the intrinsic resistance of
the power supply again.
6
7. Figure. 8: diagram of charging currents
Figure. 7: charging currents path
Figure 9: discharging currents path
Figure. 10: diagram of discharging currents
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The function of thyratron is to act
as an electronic switch which
requires a positive trigger of only
150 volts. The thyratron requires a
sharp leading edge for a trigger
pulse and depends on a sudden
drop in anode voltage (controlled
by the pulse- forming network) to
terminate the pulse and cut off the
tube. The R-C combination acts
as a DC- shield and protect the
grid of the thyratron. This trigger
pulse initiates the ionization of the
complete thyratron by the
charging voltage. This ionization
allows conduction from the
charged pulse-forming network through pulse transformer. The output pulse is then applied to an
oscillating device, such as a magnetron.
The Charge Path
The charge path includes the primary of the pulse
transformer, the dc power supply, and the
charging impedance. The thyratron (as the
modulator switching device) is an open circuit in
the time between the trigger pulses. Therefore it
is shown as an open switch in the Figure.
Once the power supply is switched
on (look at the dark green voltage
jump in the following diagram), the
current flows through the charging
diode and the charging impedance,
charges the condensers of the
pulse forming network (PFN). The
coils of the PFN are not yet
functional. However, the induction
of the charging impedance offers a
great inductive resistance to the
current and builds up a strong
magnetic field. The charging of the
condensers follows an exponential
function (line drawing green). The
self- induction of the charging
impedance overlaps for this.
The Discharge Path
When a positive trigger pulse is applied to the grid of
the thyratron, the tube ionizes causing the pulse-
forming network to discharge through the thyratron
and the primary of the pulse transformer. (The
tyratron is „fired”)
The fired thyratron grounds the pulse line at the
charging coil and the charging diode effectively.
Therefore, a current flows for the duration PW
through the pulse transformer primary coil to ground
and from ground through the thyratron, which is now
7
8. Figure 11: Thyratron
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conducting to the other side of the pulse forming network. The high voltage pulse for the
transmitting tube can be taken on the secondary coil of the pulse transformer. Exactly for this
time an oscillating device swings on the transmit frequency. Because of the inductive properties
of the PFN, the positive discharge voltage has a tendency to swing negative.
If the oscillator and pulse transformer circuit impedance is properly matched to the line
impedance, the voltage pulse that appears across the transformer primary equals one-half the
voltage to which the line was initially charged.
Thyratron
A typical thyratron is a gas-filled tube for radar modulators. The function of the high-vacuum tube
modulator is to act as a switch to turn a pulse ON and OFF at the transmitter in response to a
control signal.
The grid has complete control over the initiation of cathode emission
for a wide range of voltages. The anode is completely shielded from
the cathode by the grid. Thus, effective grid action results in very
smooth firing over a wide range of anode voltages and repetition
frequencies. Unlike most other thyratrons, the positive grid-control
characteristic ensures stable operation. In addition, deionization time
is reduced by using the hydrogen-filled tube.
A trigger pulse ionize the gas between the anode and the cathode.
Only by removing the plate potential or reducing it to the point where
the electrons do not have enough energy to produce ionization will
tube conduction and the production of positive ions stop. Only after
the production of positive ions is stopped will the grid be able to
regain control.
Because of the very high anode voltage the anode is attached most
on the upper end of the glass bulb. Therefore the tube looks very
ancient. By the ionized gas it shines in the ionizated condition like a
glow lamp.
Note: The condensers in a modulator have got a high capacity. There are very high death-
trap voltages retained after the off-switching of the device. During maintenance near
the modulator, these condensers are to dischanged!
8
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Fully Coherent Radar
Figure 12: An easy block diagram of a fully coherent radar
The block diagram on the figure illustrates the principle of a fully coherent radar. The fundamental
feature is that all signals are derived at low level and the output device serves only as an
amplifier. All the signals are generated by one master timing source, usually a synthesiser, which
provides the optimum phase coherence for the whole system. The output device would typically
be a klystron, TWT or solid state. Fully coherent radars exhibit none of the drawbacks of the
pseudo-coherent radars, which we studied in the previous section. Additional devices have the
following function:
Master
Oscillator
The Master Oscillator is a very stable CW (Continuous Wave) crystal oscillator and constitutes
the internal phase reference. It provides the coherent reference signal to the Phase Sensitive
Detector and also through a frequency divider generates the system PRF in the Synchronizer.
Mixer/
Exciter
The function of this mixer stage is to convert the StaLO- Frequency and the Master Oscillator
frequency upwards into the phase-stabile continuous wave transmitter-frequency. Any
changing of the operating frequency
Waveform-
Generator
The Waveform-Generator generates the transmitting pulse in low- power. It generates the
transmitting signal on an IF- frequency. It permits generating predefined waveforms by driving
the amplitudes and phase shifts of carried microwave signals. These signals may have a
complex structure for a pulse compression.The IF-pulses are mixed with the Exciter frequency
to the low-power microwave pulses.
Power
Amplifier
In this system the transmitting pulse is caused with a small performance in a waveform
generator. It is taken to the necessary power with a Power Amplifier followingly. The Power
Amplifier would typically be a klystron, Traveling Wave Tube (TWT) or solid state.
9
10. Figure 13: Solid state amplifier of the ATC-radar ASR-E
(Manufacturer: EADS)
Figure 14: Schematic diagram of a power-modul for solid-state transmitter
Figure 15: GaAs-MeSFET
Transistor in MMIC
Technology
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Solid State Transmitter
The PSR transmitter of the ATC-radar ASR-E
(Manufacturer: EADS) operates in the S-Band
(2.7 … 2.9 GHz) and is solid state. It comprises four
clusters, each of which contains eight power modules.
All power modules are identical. BITE and status
information are displayed on the transmitter front
panel, as well as at the operator workstation. The
modules can be replaced during transmitter operation
(hot replacement) without the disconnection of any
cables.
All high power transistors are protected against
consequential damage. The availability of the
transmitter is nearly 100% because of the graceful
degradation capability. The unservicability of one or
more power modules will not cause the complete loss of the transmitter and consequently of the
ASR-E system. A temporary slight reduction in performance has, however, to be accepted. Driver
and power supply modules are also redundant.
Power Modules
Solid State transmitters are
employed in radar sets nowadays
however too. At constant phases
several MESFET- power amplifiers
operates parallelly by means of
simple power splitters and adders.
The high performance is assembled
by many low-power amplifiers (or
amplifier modules). The modules are
feed in phase by power splitters. Its
respective output powers then are in
phase summed up to the complete
transmit power. To achieve adequate
range with relatively low pulse power, the pulses are intra-pulse
modulated often. The technology of pulse compression we will discuss
later.
GaAs-MESFETs are more often used by radar sets in solid state high
power amplifiers. MMIC- technology (Monolithic Microwave Integrated
Circuit) is a semiconductor process technology. It can be used to
obtain active elements on the same silicon substrate. These circuits
can be used up to very high frequencies.
Waveform-Generator
A waveform generator generates the transmitting signal on an IF- frequency. It permits
generating predefined waveforms by driving the amplitudes and phase shifts of carried
microwave signals. These signals may have a complex structure for a pulse compression. Since
these signals are used as a reference for the receiver channels too, there are high requirements
for the frequency stability.
10
11. „Radartutorial“ (www.radartutorial.eu)
Figure 16: an e.g. Block diagram of a waveform generator for a non-linear compressed pulse
The finally waveform is constructed of 2048 discrete voltage steps here. Its values of amplitude
and phase are stored in programmable memories (PROM's). The processing of an I & Q- phase-
detector is arranged reverse virtually.
This method of design the transmitting pulses hats got the advantage, that the waveform is
digitally described for a computer-controlled signal processing. A digital processor unit can
execute the pulse compression now.
Clock-Pin The external clock of 25 Megahertzes clocks the counter-cascade.
WF-Start-Pin The trailing edge of the negative polarized “WF-Start”-Pulse triggers the flip-flop. The output
enables the counter-cascade. It begins to count the clock pulses.
The flip-flop set by the „WF-Start”-Pulse generates an enable-signal for the counter-cascade. The
carry-pulse of the counters resets the flip-flop and the counter stops.
11-Bit
Counter
The counter-cascade counts the clock pulses and generates the 11 adress bits for the memories.
One loop of the counter-cascade stand for the pulsewidth of the transmitting pulse and take a time
of approximately 40 microseconds.
Carry-Signal
to Reset
The carry pulse of the counter-cascade resets the flip-flop and the counter stops to count.
11-Bit
Adress-Bus
There are 11 adress bits for adressing the memories..
Sine- PROM The whole waveform is divided into 2048 timesteps. For every timestep a 8-bit voltage value is
stored in this programmable memory. This memory provides the sine wave (the In-Phase signal).
Cosine-
PROM
This memory provides the cosine wave (the Quadrature signal).
D/A-
Converter
This D/A-Converter converts the 8-Bit data words into an analogue voltage. All these timesteps got
an different value of voltage and these timesteps are stringed to a frequency together. The
frequency can reach values from zero (DC) to 1 megahertz.
F1 Local
Oszillator
This jack supplies with the unmodulated IF from an external F1 local oscillator.
Amplifier This amplifier decouples the D/A-Converter from the load (the mixer).
Mixer The mixer alloys the unmodulated IF-frequency and the frequencies of the modulation to the IF-
Waveform.
Hybrid-
Combiner
The Hybrid-Combiner is a passive pover divider intrinsically, but used „on backwards”. The both
input-signals are combined phase-dependent to the finally IF- waveform of the transmitting pulse.
Waveform-
Amplifier
This amplifier is a decoupler and a band pass filter simultaneously to block out the harmonic waves.
11
12. Figure 17: a linear frequency
modulated pulse
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Pulse Compression
Intra-pulse modulation and pulse compression are generic terms that are used to describe a
wave-shaping process that is produced as a propagating waveform, and is modified by the
electrical network properties of the transmission line. The pulse is frequency or phase modulated,
which provides a method to further resolve targets which may have overlapping returns. Pulse
compression originated with the desire to amplify the transmitted
impulse (peak) power by temporal compression. It is a method
which combines the high energy of a long pulse width with the high
resolution of a short pulse width. The pulse structure of a linear
frequency modulated pulse is shown in the figure 17.
Since each part of the pulse has unique frequency, the returns can
be completely separated.
This modulation or coding can be either
• FM (frequency modulation)
o linear (chirp radar) or
o non-linear as
o symmetric form
o non-symmetric form
• PM (phase coded modulation).
Now the receiver is able to separate targets with overlapping of noise. The received echo is
processed in the receiver by the compression filter. The compression filter readjusts the relative
phases of the frequency components so that a narrow or compressed pulse is again produced.
The radar therefore obtains a better maximum range than it is expected because of the
conventional radar equation.
The ability of the receiver to improve the range resolution over that of the conventional system is
called the pulse compression ratio (PCR). For example a pulse compression ratio of 50:1 means
that the system range resolution is reduced by 1/50 of the conventional system.
Alternatively, the factor of improvement is given the symbol PCR, which can be used as a
number in the range resolution formula, which now becomes:
( )0 Pw 2 PCRresR c= ⋅ ⋅ ⋅ (1)
The compression ratio is equal to the number of sub pulses in the waveform, i.e., the number of
elements in the code. The range resolution is therefore proportional to the time duration of one
element of the code. The maximum range is increased by the PCR.
The minimum range is not improved by the process. The full pulse width still applies to the
transmission, which requires the duplexer to remained aligned to the transmitter throughout the
pulse. Therefore Rmin is unaffected.
Advantages Disadvantages
lower pulse-power high wiring effort
higher maximum range bad minimum range
good range resolution time-sidelobes
better jamming immunity needs higher processing power
difficulty reconnaissance
12
13. Figure 17: Block diagram for an analogue pulse-compression wiring
Figure 18: SAW- device width linear decreased spacing of the
transducers
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Pulse compression with linear FM waveform
At this pulse compression
method the transmitting pulse
has a linear FM waveform. This
has the advantage that the
wiring still can relatively be kept
simple. However, the linear
frequency modulation has the
disadvantage that jamming
signals can be produced
relatively easily by so-called
„Sweeper”.
The block diagram on the
picture illustrates, in more
detail, the principles of a pulse
compression filter.
The compression filter are
simply dispersive delay lines with a delay, which is a linear function of the frequency. The
compression filter allows the end of the pulse to „catch up” to the beginning, and produces a
narrower output pulse with a higher amplitude. As an example of an application of the pulse
compression with linear FM waveform the air defence radar family of AN/FPS-117 can be
mentioned.
Filters for linear FM pulse compression radars are now based on two main types.
• Digital processing (following of the A/D- conversion).
• Surface acoustic wave (SAW) devices.
SAW- Devices
SAW devices (Surface Acoustic Wave) are
extensively deployed in currently using the
pulse compression operational systems.
They are built on a piezoelectric substrate,
which propagates acoustic waves along the
surface.
The low speed of the waves means that
significant delays can be implemented in a
small space. The inter digital transducers convert the electrical signal to acoustic waves and are
made of metallic thin films deposited on the substrate. It is clearly easy to fabricate the required
shapes by photographic etching techniques. The frequency response of the delay line depends
on the spacing of these transducers.
In the example shown, the received pulse is input at the left hand and the compressed output
pulse results at the right hand end. The highest frequency suffers the largest delay and overlays
the lowest frequency. All frequency parts of the input signal are slid into the same Rangecell.
The presence of harmonics in the signal input will hamper the output waveform of each filter. The
output of the compression filter consists of the compressed pulse accompanied by responses at
other times (i.e., at other ranges), called time or range sidelobes. SAW- Filter (Surface Acoustic
Wave) werden oft in Radarsystemen mit Pulskompression eingesetzt und komprimieren das
frequenzmodulierte Echosignal auf analogem Wege
13
14. Figure 19: View of the Time-Side-Lobes
Figure 20: symmetric form
Figure 21: non-symmetric form
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Time-Side-Lobes
The output of the compression filter consists of the
compressed pulse accompanied by responses at other times
(i.e., at other ranges), called time or range sidelobes. The
figure shows a view of the compressed pulse of a chirp radar
at an oscilloscope and at a ppi-scope sector.
Amplitude weighting of the output signals may be used to
reduce the time sidelobes to an acceptable level. Weighting
on reception only results a filter „mismatch” and some loss of
signal to noise ratio.
The sidelobe levels are an important parameter when
specifying a pulse compression radar. The application of weighting functions can reduce time
sidelobes to the order of 30 db's.
Pulse compression with non-linear FM waveform
The non-linear FM waveform has several distinct advantages.
The non-linear FM waveform requires no amplitude weighting
for time-sidelobe suppression since the FM modulation of the
waveform is designed to provide the desired amplitude
spectrum, i.e., low sidelobe levels of the compressed pulse can
be achieved without using amplitude weighting.
Matched-filter reception and low sidelobes become compatible
in this design. Thus the loss in signal-to-noise ratio associated
with weighting by the usual mismatching techniques is
eliminated.
A symmetrical waveform has a frequency that increases (or
decreases) with time during the first half of the pulse and
decreases (or increases) during the last half of the pulse. A non
symmetrical waveform is obtained by using one half of a
symmetrical waveform.
The disadvantages of the non-linear FM waveform are
• Greater system complexity
• The necessity for a separate FM modulation design for
each type of pulse to achieve the required sidelobe
level.
14
Figure 22: nonn-symmetric waveform divided for two carrier frequencies
15. Bild 22: Diagramm eines Phasencodierten Sendeimpulses
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Phase-Coded Pulse Compression
Phase-coded waveforms differ from FM waveforms in that the long pulse is sub-divided into a
number of shorter sub pulses. Generally, each sub pulse corresponds with a range bin. The sub
pulses are of equal time duration; each is transmitted with a particular phase. The phase of each
sub-pulse is selected in accordance with a phase code. The most widely used type of phase
coding is binary coding..
The binary code consists of a sequence of
either +1 and -1. The phase of the transmitted
signal alternates between 0 and 180° in
accordance with the sequence of elements, in
the phase code, as shown on the figure. Since
the transmitted frequency is usually not a
multiple of the reciprocal of the sub pulsewidth,
the coded signal is generally discontinuous at
the phase-reversal points.
The selection of the so called random 0, π
phases is in fact critical. A special class of binary
codes is the optimum, or Barker, codes. They are
optimum in the sense that they provide low
sidelobes, which are all of equal magnitude. Only
a small number of these optimum codes exist.
They are shown on the beside table. A computer
based study searched for Barker codes up to
6000, and obtained only 13 as the maximum
value.
It will be noted that there are none greater than 13
which implies a maximum compression ratio of 13,
which is rather low. The sidelobe level is -22.3 db.
15
Length of
code n
Code elements
Peak-sidelobe
ratio, dB
2 + – -6.0
3 ++ – -9.5
4 ++ – + , +++ – -12.0
5 +++ – + -14.0
7 +++ – – + – -16.9
11 +++ – – – ++ – –+ – -20.8
13 +++++ – –++ – + – + -22.3