Introduction to Radar Systems Radar Transmitter/Receiver Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061902 -1 Disclaimer of Endorsement and Liability • The video courseware and accompanying viewgraphs presented on this server were prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor the Massachusetts Institute of Technology and its Lincoln Laboratory, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, products, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors or the Massachusetts Institute of Technology and its Lincoln Laboratory. • The views and opinions expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or any of their contractors or subcontractors Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -2 Outline • Introduction • Radar Transmitter • Radar Waveform Generator and Receiver • Radar Transmitter/Receiver Architecture • Summary Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -3 Radar Block Diagram We will cover this particular part of the radar in this lecture Propagation Waveform Transmitter Medium Generator Duplexer Target Cross Pulse Doppler Section Receiver A / D Antenna Compression Processing Console / Tracking & Display Detection Parameter Estimation Recording Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -4 Simplified Radar Transmitter/Receiver System Block Diagram High Power Transmit Sections Low Power Transmit Section (100’s of W to 1’s MW) (10’s of mW to 1 W) High Power Amplifier Waveform Duplexer Filter Generator Low Noise Amplifier 00101111010 Filter Receiver A/D Low Power Receive Sections (μW to mW) • Radar transmitter and receiver can be divided into two important subsystems – High power transmitter sections – Low power sections Radar waveform generator and receiver Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -5 Radar Range Equation Revisited Parameters Affected by Transmitter/Receiver • Radar range equation for search (S/N = signal to noise ratio) Pav A e σ st Pav = average power S/N= 4 Αe = antenna area R4π Ω k s T L ts = scan time for Ω Pav = average power σ = radar cross section • S/N of target can be enhanced by Ω = solid angle searched R = target range – Higher transmitted power Pav Ts = system temperature – Lower system losses L L = system loss – Minimize system temperature Ts The design of radar transmitter/receiver affects these three parameters directly Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -6 Outline • Introduction • Radar Transmitter Overview – High Power Amplifier • Radar Waveform Generator and Receiver • Radar Transmitter/Receiver Architecture • Summary Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -7 Power Amplification Process Driver Amplifier(s) Low Power Signal (from WFG) PAPA 11 PAPA 22 HPAHPA 33 PA = Power Amplifier HPA = High Power Amplifier • Amplification occurs in multiple stages – Driver amplifiers – High power amplifier • Requirement for power amplifier – Low noise – Minimum distortion to input signal Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -8 Method to Obtain Higher Power High Power Combiner HPA Antenna Antenna Driver Amp. Driver Amp. Waveform Waveform Σ HPA Generator Generator 1 – Single amplifier transmitter 2 – Parallel combining of HPA’s Single antenna Single antenna • Higher transmitted power can be obtained by combining multiple amplifiers in parallel – Lower efficiency (due to combiner losses) – Increased complexity HPA = High Power Amplifier Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -9 Types of High Power Amplifiers • Vacuum tube amplifiers and solid state amplifiers Vacuum Tube Solid State Amplifiers Amplifiers High Low Output Power (10 kW to 1 MW) (10’s to 100’s W) High Low Cost per Unit ($10’s K to $300 K) ($100’s ) Cost per Watt $1 – 3 Varied Size Bulky and heavy Small foot print • Dish antenna • Active array Applications • Passive array • Digital array Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -10 Average Power Output Versus Frequency Tube Amplifiers versus Solid State Amplifiers 106 Tube Amplifiers Dominate 104 Region of Competition 102 Solid State Amplifiers Dominate 1 Average Power (Watts) 10-2 .1 1 10 100 1000 Frequency (GHz) Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -11 Power Amplifier Examples • Tube amplifiers – Klystrons – Travelling wave tubes • Solid State amplifiers – Solid state power transistors Criteria for choosing high power amplifier – Average power output as a function of frequency – Total bandwidth of operation – Duty cycle – Gain – Mean time between failure (MTBF) – etc… Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -12 MIT/LL Millstone Hill Radar Klystron Tubes (Vacuum Devices) Output device Klystrons (2) Center Frequency 1295 MHz Bandwidth 8 MHz Peak Power 3 MW Average Power 120 kW Pulse Width 1 ms Beam Width 0.6o Antenna Diameter 84 ft •• OriginallyOriginally designeddesigned inin earlyearly 1960’s1960’s Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -13 How Big are High Power Klystron Tubes ? Millstone Hill Radar Transmitter Room VarianVarian X780X780 KlystronKlystron •• $400,000/tube$400,000/tube Waveguide output •• 77 ftft (height)(height) xx 1ft1ft (diameter)(diameter) •• 600600 lbslbs •• 3%3% dutyduty cyclecycle •• 4242 dBdB gaingain Waveguide Harmonic Filter •• 600W600W peakpeak inputinput drivedrive levellevel Flex Waveguide Output flanges 200’ Spare Tube antenna waveguide Vacuum Pump Water Coolant Hoses, 70 Gal/min Power Amplifier Room 1 kW Peak Solid State Driver Amp. Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -14 Photograph of Traveling Wave Tubes Another Type of Tube Amplifiers S Band X Band VTS-5753 VTX-5681C Center Freq : 3.3 GHz COUPLED CAVITY COUPLED CAVITY Center Freq : 10.0 GHz Bandwidth : 400 MHz TWT TWT Bandwidth : 1 GHz Peak Power : 160 kW Peak Power : 100 kW Duty Cycle : 8 % Duty Cycle : 35 % Gain : 43 dB Gain : 50 dB ~ 8 ft S-Band Transmitter Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -15 Example of Solid State Transmitter Radar Surveillance Technology Experimental Radar (RSTER) Driver Amp Module Power Amp Module •• 1414 channelschannels withwith 140140 kWkW totaltotal peakpeak powerpower –– 88 kWkW averageaverage powerpower •• EachEach channelchannel isis suppliedsupplied byby aa powerpower amplifieramplifier modulemodule –– 1010 kWkW peakpeak powerpower Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -16 Solid State Active Phased Array Radar PAVE PAWS • PAVE PAWS – First all solid state active aperture electronically steered phased array radar – UHF Band – 1792 active transceiver T/R modules, 340 W of peak power each Courtesy of Raytheon. Used with permission. Courtesy of Raytheon. Used with permission. Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -17 Outline • Introduction • Radar Transmitter Overview – High Power Amplifier – Duplexer • Radar Waveform Generator and Receiver • Radar Transmitter/Receiver Architecture • Summary Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -18 Radar Transmitter/Receiver Timeline Pulse Width High Power Pulse Receive Window A/D Samples Receiver Radar PRI Duplexer Switch Transmit Receive Transmit Receive • Sensitive radar receiver must be isolated from the powerful radar transmitter – Transmitted power typically 10 kW – 1 MW – Receiver signal power in 10’s μW – 1 mW • Isolation provided by duplexer switching PRI = Pulse Repetition Interval Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -19 Duplexer Function Antenna Duplexer HPA • Transmitter ON – Connect antenna to X transmitter with low loss Limiter/Limiter/ Receiver – Protect receiver during SwitchSwitch transmit interval Transmit Interval • Receiver ON – Connect Antenna to receiver with low loss Antenna – (transmitter must be turned off in this interval) Duplexer X HPA – Limiter/switch is used for additional protection against strong interference Limiter/Limiter/ Receiver SwitchSwitch Receive Interval HPA = High Power Amplifier Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -20 Outline • Introduction • Radar Transmitter Overview • Radar Waveform Generator and Receiver • Radar Transmitter/Receiver Architecture • Summary Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -21 Simplified Functional Descriptions Waveform Generator Waveform Amplify Upconvert Filtering To Antenna Generation Carrier Signal 10011110010 From Antenna A/D Amplify Downconvert Filtering Receiver • Waveform generator and receiver share several similar functions – Amplification, filtering and frequency conversion Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -22 Frequency Conversion Concepts Waveform Generator Receiver Frequency Upconversion Frequency Downconversion Baseband to L Band L Band to Baseband Waveform Up L Band L Band Down 0.1 GHz 0.1 GHz Converter 1.5 GHz 1.5 GHz Converter To A/D Local Oscillator Local Oscillator 1.4 GHz 1.4 GHz • Upconverter translates the • Downconverter translates waveform frequency