radar basics

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  • Pulse - RADAR transmits a series of pulses separated by non-transmission intervals during which the radar “listens” for a return. Continuous Wave - Constantly emitting radar. Relative motion of either the radar or the target is required to indicate target position. Frequency shift.
  • 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 .
  • 1. Doppler frequency shift describes the effect that motion has on a reflected frequency. 2. Use the diagram to show: a. If the wall is moving away a ball will have to travel farther than the previous ball so the reflected balls are further apart. b. If the wall is moving toward, a ball will have to travel a shorter distance than the previous ball so the reflected balls are closer together. 3. If you assume that each ball represents the top of a wave so the distance between each ball represents a wave cycle then you find: a. The frequency of the echo is lower if the target is moving away. b. The frequency of the echo is higher if the target is coming towards. ** This is why the sound of a passing train or airplane goes from higher pitch to lower pitch. 4. Key Points: 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 greater the frequency shift.
  • Make copies for distribution. 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, eliminates impossible signals. b. The unit will only allow certain frequency bands so won’t process stray signals. 6. Indicator. Displays data. Displays velocity or the component directly 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.
  • Discuss Slide Range for CW: (p. 106) Frequency Modulated Continuous Wave. Altitude for CW: Slant range (see coming slide)
  • Pg. 72 Fig 2-39 1. Discuss displays, time permitting.
  • radar basics

    1. 1. RadarRadar && its Classificationits Classification by: Himank Charayaby: Himank Charaya
    2. 2. OutlineOutline 1.1. Introduction to radar .Introduction to radar . 2.2. Radar classification.Radar classification. 3.3. Continous wave radar.Continous wave radar. 4.4. Doppler effect.Doppler effect. 5.5. Frequency-modulated CW radar.Frequency-modulated CW radar.
    3. 3. RADARRADAR What is RADAR an acronym for?What is RADAR an acronym for? Radio Detection and Ranging.Radio Detection and Ranging. Radio wave is generated, transmitted,Radio wave is generated, transmitted, reflected, and detected.reflected, and detected. RADAR unimpaired by night, fog,RADAR unimpaired by night, fog, clouds, smokeclouds, smoke RADAR is good for isolated targetsRADAR is good for isolated targets against a relatively featurelessagainst a relatively featureless background.background.
    4. 4. The components of a radar system.The components of a radar system. 1. Transmitter 2. Antenna 3. Receiver 4. Display unit 5. Power supply 6. Duplexer( improved radar).
    5. 5. Two Basic Radar TypesTwo Basic Radar Types Pulse TransmissionPulse Transmission Continuous WaveContinuous Wave
    6. 6. Pulse TransmissionPulse Transmission
    7. 7. Continuous Wave RadarContinuous Wave Radar Employs continualEmploys continual RADAR transmissionRADAR transmission Separate transmit andSeparate transmit and receive antennasreceive antennas Relies on theRelies on the “DOPPLER SHIFT”“DOPPLER SHIFT”
    8. 8. Continuous Wave RadarContinuous Wave Radar Continuous wave (CW) radarsContinuous wave (CW) radars typically determine target velocity,typically determine target velocity, and can achieve considerable rangesand can achieve considerable ranges without the high peak power. Thesewithout the high peak power. These radars are typically simpler, moreradars are typically simpler, more compact and less costly.compact and less costly.
    9. 9. Doppler EffectDoppler Effect that the Doppler effect is the change inthat the Doppler effect is the change in frequency that occurs when a sourcefrequency that occurs when a source and a target are in relative motion.and a target are in relative motion. The Doppler affect can be used in aThe Doppler affect can be used in a CW radar in order to determineCW radar in order to determine velocity.velocity.
    10. 10. Doppler effect theoryDoppler effect theory FFd=d= 2V2Vrr λλ FFd =d = doppler shiftdoppler shift VVrr = relative velocity of target with= relative velocity of target with respect to radar.respect to radar.
    11. 11. Doppler Frequency ShiftsDoppler Frequency Shifts Motion Away: Echo Frequency Decreases Motion Towards: Echo Frequency Increases
    12. 12. Continuous Wave RadarContinuous Wave Radar ComponentsComponents Discriminator AMP Mixer CW RF Oscillator Indicator OUTOUT ININ Transmitter Antenna Antenna
    13. 13. FM-CW radarFM-CW radar An unmodulated CW radar isAn unmodulated CW radar is incapable of detecting range, as thereincapable of detecting range, as there is no reference point in the transmittedis no reference point in the transmitted or returned signal for measuringor returned signal for measuring elapsed time.elapsed time. By frequency modulating the CW signal,By frequency modulating the CW signal, differences between the transmitted anddifferences between the transmitted and received frequencies can be used to estimatereceived frequencies can be used to estimate range.range.
    14. 14. Pulse Vs. Continuous WavePulse Vs. Continuous Wave Pulse EchoPulse Echo Single AntennaSingle Antenna Gives Range,Gives Range, usually Alt. as wellusually Alt. as well Susceptible ToSusceptible To JammingJamming Physical RangePhysical Range Determined By PWDetermined By PW and PRF.and PRF. Continuous WaveContinuous Wave Requires 2 AntennaeRequires 2 Antennae Range or Alt. InfoRange or Alt. Info High SNRHigh SNR More Difficult to JamMore Difficult to Jam But Easily DeceivedBut Easily Deceived Amp can be tuned toAmp can be tuned to look for expectedlook for expected frequenciesfrequencies
    15. 15. Specific Types of RadarSpecific Types of Radar Frequency Modulated CW RadarFrequency Modulated CW Radar Use for radar altimeters and missile guidance. Pulse DopplerPulse Doppler Carrier wave frequency within pulse is compared with a reference signal to detect moving targets. Moving Target Indicator (MTI) SystemMoving Target Indicator (MTI) System Signals compared with previous return to enhance moving targets. (search radars) Frequency Agile SystemsFrequency Agile Systems Difficult to jam.
    16. 16. Thank you.Thank you.

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