Transcription of Radar Systems Engineering Lecture 17 Transmitters …
1 IEEE New Hampshire SectionRadar Systems Course 1 XMTR & RCVR 1/1/2010 IEEE AES SocietyRadar Systems Engineering Lecture 17 Transmitters & ReceiversDr. Robert M. O DonnellIEEE New Hampshire SectionGuest Lecturer Radar Systems Course 2 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyPulseCompressionReceiverClutter Rejection(Doppler Filtering)A / DConverterBlock Diagram of Radar SystemAntennaPropagationMediumTargetRada rCrossSectionTransmitterGeneral Purpose ComputerTrackingDataRecordingParameterEs timation WaveformGenerationDetectionPowerAmplifie rT / RSwitchSignal Processor ComputerThresholdingUser Displays and Radar ControlPhoto ImageCourtesy of US Air ForceThis Lecture will cover all of the subsystems in the red dashed boxRadar Systems Course 3 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyRadar Range Equation Revisited Parameters Affected by transmitter /Receiver Radar range equation for search (S/N = signal to)
2 Noise ratio) S/N of target can be enhanced by Higher transmitted power Pav Lower system losses L Minimize system temperature Ts L T k R 4 t AP S/Ns4seav =The design of Radar transmitter /receiver affects these three parameters directlyPav = average power e = antenna areats = scan time for Pav = average power = Radar cross section = solid angle searchedR = target rangeTs = system temperatureL = system lossCourtesy of MIT Lincoln LaboratoryUsed with PermissionRadar Systems Course 4 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyOutline Transmitters Receivers and Waveform
3 Generators Other transmitter / Receiver Subsystems Radar Receiver- transmitter Architectures SummaryRadar Systems Course 5 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyOutline Transmitters Introduction Block Diagram High Power Tube Amplifiers Klystron Traveling Wave Tube Crossed Field Amplifier Magnetron Solid State RF Power Amplifiers T/R Modules Receivers and Waveform Generators Other transmitter / Receiver Subsystems Radar Receiver- transmitter Architectures SummaryRadar Systems Course 6 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyIntroduction Ideal transmitter Provides sufficient energy to detect the target Easily modulated to produce desired waveforms Generate stable noise free signal for good clutter rejection Provide needed tunable bandwidth High efficiency High reliability Easily maintainable Long life Small and light weight for the intended application Affordable Obviously compromise is necessary !
4 Radar Systems Course 7 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietySimplified Radar transmitter /Receiver System Block DiagramReceiverLNAF ilterA/DCovertersHPAF ilterDuplexerWaveformGeneratorHigh Power Transmit Sections(~100 W to ~MW)Low Power Transmit Section(~100mw to ~1W) Radar transmitter and receiver can be divided into two major subsystems: Low power transmit and receive sections Radar waveform generator and receiver High power transmitter sectionsLow Power Receive Sections(~ w to ~mW)ToSignalProcessorHPA = High Power AmplifierLNA = Low Noise AmplifierRadar Systems Course 8 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyBlock Diagram of High Power Tube TransmitterCrowbarUnitHigh VoltageSwitch GearSCRC ontrollerHigh VoltagePower Supply& RectifierCapacitorBank andRegulatorHigh VoltagePulseModulatorHigh PowerAmplifier TubeandSolenoidTransmitterProtectionSyst emRF IPA& MicrowaveNetworkFaultLogic UnitTransmitterControlSystemTransmitterC onsoleHigh VoltageSectionPrimaryPowerSourceTransmit ter andSystem InputsHighPowerRFOutputTransmitterContro lConsole
5 &TransmitterProtectionSystemTransmitter Gating /TimingTransmitterFunctionsRF InputSystem TimingandTransmitter InputsTransmitterInputsControl SectionHigh DC Voltage, High Power InputPulseModulatorPowerAmplifierIPA=Int ermediate Power AmplifierRadar Systems Course 9 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyOutline Introduction Transmitters Introduction Block Diagram High Power Tube Amplifiers Klystron Traveling Wave Tube Crossed Field Amplifier Magnetron Solid State RF Power Amplifiers T/R Modules Receivers and Waveform Generators Radar Receiver- transmitter Architectures SummaryRadar Systems Course 10 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyKlystron High Power Amplifier First developed in early 1950s
6 Bandwidth as great as 12% RF conversion efficiency 35 - 50% Coherent- pulse to pulseThree Cavity KlystronCollectorRF CavitiesRFOutRFInCathodeHeaterAnodeModul atingAnodeDriftSpaceElectron BeamCollectorInteraction GapsRF SectionElectron GunAdapted from SkolnikReference 1 Radar Systems Course 11 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyKlystron How It Works Electron gun generates electron beam (X rays produced/shielding required) RF section composed of several resonators (resonant cavities) RF is coupled in by waveguide through slot in cavity or coax RF input is used to modulate the electron stream into bunches Resonant frequency of cavity is identical to RF input frequency causing cavity to oscillate Oscillations in electric field modulate speed of electron beam into bunches Resonant cavity at output extracts the RF power from the density modulated beam and delivers power to output transmission lineRF CavitiesRF InRF OutCollectorElectron BeamElectron GunAdapted from SkolnikReference 1 Radar Systems Course 12 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES
7 SocietyExample S-Band KlystronVA-87F / VKS-8287 Air Surveillance / Weather Radar 6 cavity, S BandTunable over to GHzPeak Power up to MWAve Power up to 3 kWGain 50 dB Efficiency 45 %Bandwidth 30 MHz Duration up to secCourtesy of CPI. Used with Systems Course 13 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyMIT/LL Millstone Hill Radar Klystron Tubes (Vacuum Devices) Originally designed in early 1960 s Originally designed in early 1960 sOutput deviceKlystrons (2)Center Frequency1295 MHzBandwidth8 MHzPeak Power3 MWAverage Power120 kWPulse Width1 msBeam Width Diameter84 ftCourtesy of MIT Lincoln LaboratoryUsed with PermissionRadar Systems Course 14 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyHow Big are High Power Klystron Tubes ?
8 Millstone Hill Radar transmitter Room1 kW Peak Solid State Driver Amplifier RoomFlex Waveguide Output flangesWaveguide Harmonic Filter200 antenna waveguideWater Coolant Hoses, 70 Gal/minWaveguide outputVarian X780 Klystron $400,000/tube 7 ft (height) x 1ft (diameter) 600 lbs 3% duty cycle 42 dB gain 600W peak input drive levelVarian X780 Klystron $400,000/tube 7 ft (height) x 1ft (diameter) 600 lbs 3% duty cycle 42 dB gain 600W peak input drive levelVacuum PumpSpare TubeCourtesy of MIT Lincoln LaboratoryUsed with PermissionRadar Systems Course 15 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyTraveling Wave Tube Capable of wide bandwidth at high power Expensive Similar to Klystron, linear beam tubes Interaction between RF field and electron beam over length of tube RF wave mixes with electron beam and transfers DC energy from electron beam to increase energy of RF wave.
9 Causing wave to be amplifiedCathodeElectron BeamGun AnodeHelix InteractionRegionHeaterRF InCollectorAttenuationRF OutAdapted from SkolnikReference 1 Radar Systems Course 16 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyPhotograph of Traveling Wave Tubes Another Type of Tube AmplifiersX BandVTX-5681C COUPLED CAVITYTWTC enter Freq : GHzBandwidth : 1 GHzPeak Power : 100 kW Duty Cycle : 35 %Gain : 50 dBS BandVTS-5753 COUPLED CAVITYTWTC enter Freq : GHzBandwidth : 400 MHz Peak Power : 160 kWDuty Cycle : 8 %Gain : 43 dB~ 8 ftS-Band transmitter Courtesy of MIT Lincoln LaboratoryUsed with PermissionRadar Systems Course 17 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyCrossed Field Amplifier (CFA) Capable of.
10 High coherent power Good efficiency Wide bandwidth Relatively low gain (10 dB) Generally noisier and less stableSimplifiedRepresentationof CFA Resembles magnetron and employs crossed electric and magnetic fields Electrons emitted from cylindrical cathode Under action of crossed electromagnetic fields, electrons form rotating bunches Bunches of electrons drift in phase with RF signal and transfer their DC energy to the RF wave to produce amplificationCathodeAnodeandSlow-waveCir cuitControlElectrodeRFInDriftRegionRFOut Radar Systems Course 18 XMTR & RCVR 1/1/2010 IEEE New Hampshire SectionIEEE AES SocietyCrossed Field AmplifierX-Band ( to GHZ)
