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Home , Signal, Transmitter

Introduction to Systems

Radar /Receiver

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061902 -1 Disclaimer of Endorsement and Liability

• The 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 , 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 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 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 Transmit Sections Low Power Transmit Section (100’s of W to 1’s MW) (10’s of mW to 1 W)

High Power

Waveform Filter Generator

Low 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 = to noise ratio)

t AP t seav σ Pav = average power S/N = 4 Αe = antenna area L T k R 4π Ω R k T s 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 – High power amplifier • Requirement for power amplifier – Low noise – Minimum 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

• 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 $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 Tube Amplifiers versus Solid State Amplifiers

106

Tube Amplifiers Dominate 104 Region of Competition

102

Solid State Amplifiers Dominate 1 Average Power ()

10-2 .1 1 10 100 1000 Frequency (GHz)

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -11 Power Amplifier Examples

• Tube amplifiers – – Travelling tubes

• Solid State amplifiers – Solid state power

Criteria for choosing high power amplifier – Average power output as a of frequency – Total of operation – Duty cycle – – Mean time between failure (MTBF) – etc…

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -12 MIT/LL Millstone Hill Radar 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 Radar PAVE PAWS

• PAVE PAWS – First all solid state active aperture electronically steered phased array radar – UHF Band – 1792 active 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 to a the receive frequency to a higher frequency lower frequency • Reason: • Reason: – Waveform generation – of A/D less expensive at lower converter higher at lower frequency frequency

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -23 Simplified System Block Diagram Waveform Generator and Receiver

Waveform Generator 1.5 GHz HPA 0.1 GHz (L-Band) Up Waveform Duplexer Filtering Filtering A converter Generation 1.4 GHz

Local Oscillator

1.5 GHz Low Noise 1.4 GHz (L-Band) Amplifier 0.1 GHz Down 0010110100 Filtering A/D Filtering converter A

Receiver

• This example shows only a single stage conversion – In general, design based on multiple stage of frequency conversion are employed • Multiple stages of amplification and filtering are also used

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -24 Outline

• Introduction

• Radar Transmitter Overview

• Radar Waveform Generator and Receiver

• Radar Transmitter/Receiver Architecture

• Summary

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -25 Dish

ALCORALCOR ALTAIRALTAIR TRADEXTRADEX MMWMMW MILLSTONEMILLSTONE HAYSTACK/HAXHAYSTACK/HAX KWAJALEIN

Waveform Duplexer Transmitter Generator

001011110100 Receiver A/D

• Conventional radar transmitter/receiver design employed

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -26 Radar Antenna Architecture Comparison

Dish Radar Passive Array Radar Active Array Radar

T/R Modules

T R T R T R O • Very low cost • Beam agility • Beam agility PR • Frequency diversity • Effective radar resource • Effective radar resource management management • Low loss • High cost • Dedicated function • Higher cost ON • Requires custom • More complex cooling C • Slow scan rate transmitter and high-power • Requires custom phase shifters transmitter • High loss • High loss

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -27 Active Phased Array Radar

HPA Low Power Section T/R Subarray Duplexer … # 1 … Receiver T/R Active T/R Module T/R Subarray … # 2 … Waveform T/R Generator

001011110100 A/D

T/R … … T/R

• Transmit/Receive function distributed to each module on array

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -28 Large Phased Arrays

Active Array Radar

Passive Array Radar THAAD Radar 25,344 elements SPY-1 4100 elements

Courtesy of Raytheon. Used with permission. Passive Array Radar

Cobra Dane 15.3K active elements

Courtesy of Raytheon. Used with permission.

Courtesy of Raytheon. Used with permission.

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -29 Digital Array Radar Architecture Digital on Receive

Subarray Analog T/R Waveform

… Σ # 1 Generator A/D

Subarray # 2 Analog T/R 001011100 … Σ 111100001 A/D Multichannel111100001 One DigitalDigital A/D Digital Beamformer BeamBeams … … (Analog Array)

… 011110100

Analog T/R

… Σ

A/D

• Each active analog T/R module is followed by an A/D for immediate – Multiple received beams are formed digitally by the digital beamformer

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -30 Digital Array Example Digital On Receive

RSTER (14 Digital Receivers)

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -31 Digital Array Radar Architecture II Digital on Transmit & Receive

001110010100 Waveform Waveform Control 1 Analog T/R Digital T/R Information

2 Analog T/R Digital T/R 001011100

111100001 Multichannel Digital

… Digital Beams Beamformer 011110100

N Analog T/R Digital T/R

• Both waveform generation and receiver digitization are performed within each T/R module – Complete flexibility on transmit and receive

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -32 Summary

• Radar transmit function is accomplished in two stages: – Waveform generator creates low power waveform signal and upconverts it to RF – Transmitter amplifies waveform signal

• Radar receiver performs filtering, amplification and downconversion functions – Final received signal is fed to an A/D for digitization

• Radar transmit/ receive architecture is highly dependent on the antenna type – Centralized architecture: dish radars, passive array radars – Distributed architecture: active array and digital array radars

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -33 References

• Skolnik, M., Introduction to Radar Systems, New York, McGraw-Hill, 3rd Edition, 2001 • Skolnik, M., Radar Handbook, New York, McGraw-Hill, 2nd Edition, 1990

Radar_TxRxCourse MIT Lincoln Laboratory PPhu 061802 -34