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Introduction to radar
Radar was originally developed for military purposes during World War 2 to detect ships and airplanes. Scientists later discovered that radar could also detect precipitation, making it an essential tool for weather prediction. There are two main types of radar: pulse radar which uses pulse transmission to determine range and continuous wave radar which relies on the Doppler effect. Key radar components include the transmitter, receiver, antenna, and display unit. Radar systems can be classified by their primary mission as search, tracking, or weather surveillance radars. Common examples include air search radars, long range surveillance radars, and tracking radars used in aircraft.
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Introduction to radar
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- 2. Functions of Radar RADARis a method of using electromagnetic waves to remote-sense the position, velocity and identifying characteristics of targets.
- 3. History of Radar Radarwas developed for military purposes during W. W. II. The British and US Military used radar to locate ships and airplanes.
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- 5. History of Radar Duringthe war, radar operators found annoying blips continually appearing on the radar screen. Scientists had not known that radar would be sensitive enough to detect precipitations. Today, radar is an essential tool for predicting and analyzing the weather.
- 6. Weather Radar Weather Surveillance Radar, designed in 1957.It became the primary radar for the weather service for nearly 40 years.
- 7. Weather Radar NSSL's first Doppler WeatherRadar located in Norman, Oklahoma. 1970's research using this radar led to NWS NEXRAD WSR- 88D radar network.
- 8. The expensive radar equipmentis protected by the sphere shaped cover. On the inside it looks similar to this:
- 9. Two Basic RadarTypes Pulse Transmission Continuous Wave
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- 11. Pulse Radar Components SynchronizerSynchronizerTransmitterTransmitter Display UnitDisplay Unit ReceiverReceiver PowerPower SupplySupply ANT.ANT.DuplexerDuplexer RFOut EchoIn Antenna Control
- 12. Pulse Transmission Pulse RepetitionTime (PRT=1/PRF) Pulse Width (PW) Length or duration of a given pulse PRT is time from beginning of one pulse to the beginning of the next PRF is frequency at which consecutive pulses are transmitted. PW can determine the radar’s minimum range resolution. PRF can determine the radar’s maximum detection range.
- 13. Continuous Wave Radar Employscontinual RADAR transmission Relies on the “DOPPLER EFFECT”
- 14. Doppler Frequency Shifts MotionAway Motion Towards Echo Frequency Decreases Echo Frequency Increases
- 15. Continuous Wave Radar Components DiscriminatorAMP Mixer CW RF Oscillator Indicator OUTOUT ININ Transmitter Antenna Antenna
- 16. Pulse Vs. ContinuousWave Pulse Echo Single Antenna Gives Range & Alt. Susceptible To Jamming Physical Range Determined By PW and PRF. Continuous Wave Requires 2 Antennae No Range or Alt. Info High SNR More Difficult to Jam But Easily Deceived Amp can be tuned to look for expected frequencies
- 17. Classification by PrimaryRadar Mission Search radars and modes • Surface search • Air search • Two-dimensional search radars • Three-dimensional search radars Tracking radars and modes Track-while-scan
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- 19. AN/SPS-49 Very LongRange Air Surveillance Radar
- 20. AN/TPS-43 The AN/TPS-43 radar system,with a 200 mile range, was the only Air Force tactical ground based long range search and warning radar for nearly two decades. Most of the AN/TPS- 43 radars are being modified to the AN/TPS-75 configuration. 3-D Air Search Radar
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- 24. Tracking Radar Tracking radarsdwell on individual targets and follow their motion in azimuth, elevation,range and Doppler. Most tracking radars can follow only a single target. A few radars can track multiple targets simultaneously. An electronically steered array antenna is used so that beam positions can be moved quickly from one target to another.
- 25. AN/APG-66 in theF-16 http://www.tpub.com/neets/book 18/79j.htm
- 26. Types of Antenna Introducingtwo types of antenna reflector mirror antenna array antenna
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- 28. Parabolic Reflector Basic paraboloidreflector; Truncated paraboloid;Orange-peel paraboloid;Cylindrical paraboloid
- 29. Array Antenna An arrayantenna is composed of multiple element arrays for example, linear array, area array or nonformal array. The element antennas are half-wavelength dipoles, microstrip patches and wave guide slot. The advantages of array antenna are to enable beam scanning without changing the looking angle of each array antenna and to generate an appropriate beam shaping by selective excitation of current distribution of each element.
- 30. An Example ofArray Antenna
- 31. Edgewall Slot Array-AN/APY- 2on E-3D Aircraft The E-3 Sentry is an airborne warning and control system (AWACS) aircraft that provides all-weather surveillance, command, control and communications needed by commanders of U.S. and NATO air defense forces. As proven in Desert Storm, it is the premier air battle command and control aircraft in the world today.
- 32. Early Warning RadarArray Antenna PAWS stands for Phased Array Warning System. The radar is used primarily to detect and track sea-launched and intercontinental ballistic missiles. It can search over long distance(to 5000 km or more). Each system has two array faces 72.5 feet in diameter with 2677 element positions. To provide surveillance across the horizon, the building is constructed in the shape of a triangle. The two building faces supporting the arrays, each covering 120 degrees, will monitor 240 degrees of azimuth.
- 33. Radar Performance and FrequencyBands Bandwidth The bandwidth determines the range resolution and frequency agility capabilities of the radar. Antenna For a given gain, low frequency antennas are larger than high frequency. Low frequency are favored for long-range search applications, because of the larger effective area associated with a given gain, allowing more effective capture of echoes. Transmitter In general, more radio frequency power can be produced at low frequency than at high. Receiver There is no clear choice between high and low frequencies. Propagation The attenuation at high frequency is dramatic. A given raindrop has over three orders of magnitude more scattering cross-section at X-band(10 GHz) than at L-band(1.3 GHz), producing far more clutter and signal at the higher frequency. Targets If the wavelength is long compared to the target extent, targets are Rayleigh scatterers, and have small, non-fluctuating RCS. Summary In general, the longer the range at which the radar must detect targets, the lower the frequency of the radar.
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Editor's Notes
- #12 1. Make copies of graphic and distribute to class. 2. Synchronizer: a. Coordinates the entire system b. Determines the timing of the transmitted pulse c. Includes timers, modulator and central control. 3. Transmitter: a. Generate the pulses at the proper RF (radio frequency) for the radar. 4. Antenna: a. Receives energy from the transmitter, radiates it in the form of a highly directional beam and receives the echoes. 5. Duplexer: a. Allows one antenna to be used to transmit and receive. b. Prevents transmitted RF energy from going directly to the receiver. c. Tells the antenna to radiate or receive. 6. Receiver: receives incoming echoes from antenna, detects and amplifies the signal, and sends them to the display. 7. Display: Displays the received video to the operator. 8. Power Supply: Provides power to all the components of the system. 9. Discuss the antenna Bearing loop back to the display and its function.
- #14 Second major type of radar. Produces a constant stream of energy. Can’t distinguish distances (range) because no interval between pulses. Can distinguish between moving and non-moving targets by using Doppler frequency shifts.
- #15 a. Frequency expansion is the lowering of the echo frequency caused by an opening target (target moving away). DOWN DOPPLER b. Frequency compression is the raising of the echo frequency caused by the closing target (target moving closer). UP DOPPLER c. The moving of the transmitter can also cause frequency shifts (it’s relative motion that produces the effect). d. The faster the relative motion change the more the frequency shift.
- #16 1. Transmit/Receive Antennas. Since must operate simultaneously, must be located separately so receiving antenna doesn’t pick up transmitted signal. 2. Oscillator or Power Amplifier. Sends out signal to transmit antenna. Also sends sample signal to Mixer. (used as a reference) 3. Mixer. a. A weak sample of the transmitted RF energy is combined with the received echo signal. b. The two signal will differ because of the Doppler shift. c. The output of the mixer is a function of the difference in frequencies. 4. Amplifier. Increases strength of signal before sending it to the indicator. 5. Discriminator. a. Selects desired frequency bands for Doppler shifts. b. The unit will only allow certain frequency bands so won’t process stray signals. 6. Indicator. Displays data. Measures radial velocity or the component inbound or directly outbound. Range is not measured. 7. Filters. Used to reduce noise, used in amp to reduce sea return, land clutter, and other non-desirable targets.
- #18 There are many different radar missions, types of radars and radar modes. This is one of radar groupings.
- #19 It’s 2-D search radar. I guess it for azimuth search since it has a narrow azimuth beam and wide elevation beam.
- #20 The Radar Set AN/SPS-49 is an L-band, long-range, two-dimensional, air-search radar system that provides automatic detection and reporting of targets within its surveillance volume. The AN/SPS-49(V) radar operates in the frequency range of 850 - 942 MHZ. It shows the elevation coverage of a typical air search radar.
- #21 http://www.fas.org/man/dod-101/sys/ac/equip/an-tps-43.htm It resolves in elevation as well as azimuth. It uses multiple feeds and switches between feeds for different elevation angles. It has six stacked beams.
- #22 Array antenna
- #24 http://www.fas.org/man/dod-101/sys/ac/equip/an-tps-75.htm
- #26 The AN/APG-66 is a pulse-doppler radar designed specifically for the F-16 Fighting Falcon fighter aircraft. APG-66 uses a slotted planar-array antenna located in the aircraft's nose and has four operating frequencies within the I/J band. The system has ten operating modes, which are divided into air-to-air, air-to-surface display, and sub-modes. In the search mode APG-66 performs uplook and downlook scanning. Once a target is located via the search mode, the engagement sub-mode can be used. There are two main manual acquisition modes, single-target track and situation awareness. The situation awareness mode performs Track-While-Scan (TWS), allowing the pilot to continue observing search targets while tracking a specific target. While in this mode, the search area does not need to include the tracked target's sector.
- #29 http://www.tpub.com/neets/book11/46a.htm
- #32 Y: surveillance and control, multi-target tracking, fire control, and air control
- #33 PAVE is an Air Force program name, that, contrary to some reports, does not have an expansion, while PAWS stands for Phased Array Warning System.