Modern Radar Systems

Transcription

1 Modern Radar Systems Second Edition Hamish Meikle ARTECH HOUSE BOSTON LONDON artechhouse.com

2 Contents Foreward Preface to the second edition Preface to the first edition xvii xix xxi Chapter 1 The radar and its ground environment Primary and secondary radar Other types of radar Coordinate Systems and ränge Main monostatic radar components Transmitter Waveguide or transmission line System Diplexer Antenna Factors external to the radar Receiver Matched and matching filters Detector Analogue-to-digital converter Signal processor Threshold Determination of position Common components and timing Basic quantities, maximum ränge Secondary radar Radars with separately located transmitters and receivers Elliptical coordinates Bistatic radar maximum ränge Performance Effects on ränge Resolution Accuracy Stability 24 References 24 Chapter 2 Usual and unusual concepts An example of three-dimensional representation: the Wien bridge oscillator Vector representation Order of linear processing Polyphase modulation and demodulation Symmetrical components in polyphase circuits Harmonics in balanced polyphase circuits Polyphase, or bottle-brush, noise Time and spectral domains, helical spectra Convolution and correlation Gaussian pulses, spectra, and beam shapes Gaussian pulses and spectra Gaussian beam shapes Gaussian illumination functions Use of brackets and other symbols 50 vn

3 Vlll Modern Radar Systems References 50 Chapter 3 Transmitters Transmitter power Power Output stage Semiconductor transmitters Spectrum and sidebands Trapezoidal edges Cosine and cosine squared edges Extra modulator power needed for shaping Pulse compression Linear frequency modulation Simple phase modulation Other types of modulation and their spectra Harmonics from the transmitter Figures affecting radar Performance Range Resolution Accuracy Stability Interference to neighboring Systems 79 References 79 Chapter 4 Microwave waveguide and transmission line System Mismatch Components Coaxial cables Waveguides Strip or microstrip lines Microwave passive components Monitoring Power level Voltage Standing wave ratio (VSWR) Effect on radar Performance Effects on maximum ränge Effects on stability 96 References 96 Chapter 5 Antennas Linear and rectangular radiators Tapering the illumination function to reduce sidelobes Uniform, trapezoidal, and triangulär illumination tapering Simply tapered illumination functions Low-sidelobe tapering functions General rules for tapering Radiation from circular apertures Simply shaped circular tapering functions Circular Taylor low-sidelobe tapering function Monopulse radar antennas Tapering functions for monopulse antennas with low sidelobes Arraysofdiscrete radiators Tapered illumination functions Waysofdrivingdiscreteelements Gräting effects Beam-steering quantization effects 134

4 Contents IX 5.5 Creating shaped beams Inverse Fourier transform method The Woodward-Lawson method Circular polarization Circular polarizer for hörn feeds Reflecting polarizers Transmission polarizers Phased array polarization Engineers' and physicists' Conventions Ellipticity or the quality of circular polarization Rain echo suppression Antenna hardware losses Illumination function loss Blockingloss Spillover loss Surface tolerance loss Losses in power dividers, phase shifters, and other beam-forming network components Other effects giving losses Beam shape loss Coherent integration Noncoherent integration Small numbers of pulses Scanning loss The equivalence of different signal combining Systems Noise received from an antenna Sidelobe cancelers and adaptive beam forming Antennas mounted on aircraft Synthetic apertures Mapping Radars on satellites Other considerations Figures affecting radar Performance Range Resolution Accuracy Stability 179 References 179 Appendix 5A Mathematical appendix 180 5A. 1 Taylor distribution 180 5A.2 Zolotarev distribution 180 5A.3 Bayliss distribution 182 Chapter 6 Factors outside the radar: propagation, scattering, and clutter Amplitude and phase of the echo Amplitude of the echo Phases of the echoes and Doppler frequency Effects of the atmosphere Exponential atmosphere modeis Constant k atmosphere model Range-height paper Lens loss Anomalous propagation and superrefraction Attenuation in the atmosphere Scattering Scattering without fading Scattering with fluctuation 205

5 X Modern Radar Systems 6.4 Second-time-around effect Ground reflections and multiple paths Fiat or nearly flat earth Factors that reduce reflections and lobing Scenario to simulate a "typical" radar environment Echoes of interest, the reference echo A land clutter model The Weibull clutter model Land clutter spectrum Sea clutter Volume clutter, rain or snow clutter, and chaffor window Rain and chaff spectra Total signal at the input of the receiver Figures affecting Performance Range Accuracy Stability 251 References 251 Appendix 6A Range-height paper 253 Chapter 7 Receivers Dynamic ränge, control of gain, and sensitivity time control Radio frequency section Radio frequency amplifier Radio frequency filter Mixer Intermediate frequency amplifier and filter Limiters Effects on amplitude Effects on spectrum Receiver characteristics Minimum ränge Gain Bandwidth, filtering, ringing, and the ability to reject interference Dynamic ränge before and after sensitivity time control (STC) Ability to withstand transmitter pulse spikes Constant signal or noise Output Figures affecting radar Performance Range budget Resolution Accuracy budget Stability budget 287 References 290 Chapter 8 Matched and matching filters Uncompressed pulses Rectangular transmitter pulse and rectangular filter Rectangular transmitter pulse and Gaussian filter Doppler frequency shift, detuning Filtering after limiting, Dicke-fix receiver Pulse compression using frequency modulation Linear frequency modulation Nonlinear frequency modulation The effects of limiting before the pulse compression filter General correlator Discrete phase shift modulated pulse compression 312

6 Contents XI Binary codes Polyphase codes Other forms of modulation Negative phase sequence signals Output signals Figures affecting radar Performance Range budget Accuracy and resolution budget Stability budget 327 References 327 Chapter 9 Detectors Incoherent detectors Logarithmic intermediate frequency amplifiers Coherent detectors Ring modulator or demodulator Vector detectors Polar detectors Cartesian or two-phase detector Sampling waveforms and spectra Simple or Single phase sampling Complex or two-phase sampling Sampling at intermediate frequency Measurement of noise Gaussian noise Rayleigh noise Figures affecting radar Performance Range budget 348 References 348 Chapter 10 Analogue-to-digital conversion Principle Dynamic ränge Nature and treatment of errors Types of errors Measurement of errors Correction of errors Analogue-to-digital conversion using intermediate frequency signals Figures affecting radar Performance Range budget Accuracy and resolution budget Stability budget 360 References 361 Chapter 11 Signal processing Altering the form of the video during one sweep Limiting Differentiation of the video: fast (or short) time constant Pulse length (or width) discriminator Logarithmic video and log FTC Bandwidth or stretching of the video signals for dispiay Noise clipping Constant false alarm rate processing by cell averaging Gating the video Combining the videos from several beams 377

7 Xll Modern Radar Systems 11.2 Signal processing over a number of sweeps Video integration Binäry integration Rejection of echoes that have unwanted Doppler frequencies, moving target indicator Doppler frequency processing which selects the Doppler frequencies of interest Comparison of moving target indicators and detectors Processing over many scans and maps Area moving target indication (AMTI) or clutter map Maps for a moving target detector Quality selection Airborne moving target signal processing The TACCAR moving target indicator Displaced phase center antenna Pulse Doppler radars Sideways-looking radars Figures affecting radar Performance Range budget Accuracy and resolution budget Stability budget 444 References 444 Appendix 11A An approximation to solve for thresholds above clutter 445 Chapter 12 Threshold and detection Dwell time and the number of echoes False alarm probabilities, times, and thresholds False alarm time False alarm number False alarm probability Changing the threshold levels Probability of detection Marcum case: no fluctuation Swerling case I: slow fluctuation Swerling case II: fast fluctuation Swerling case III: slow chi-squared fluctuation Swerling case IV: fast chi-squared fluctuation Comparison of probability of detection cases Coherent integration: slow fluctuation Noncoherent integration: slow fluctuation Noncoherent integration: fast fluctuation Joint probabilities of detection Other forms of integration after the threshold Frequency diversity radars Useful approximations Albersheim's approximation for the Marcum case Snidman's approximation for the Marcum and Swerling cases Figures affecting radar Performance 487 References 487 Chapter 13 Determination of position Fire control radars Conical scanning Amplitude monopulse receivers Phase monopulse receivers Measurement of ränge Extracting the Doppler frequency 494

8 Contents X11I 13.2 Sector scan radars Fast scanning radars Surveillance radars Binary detection decisions Maximum signal Center of gravity or centroid Monopulse angle measurement with search radars Accuracy Angular accuracies and root mean square aperture Time accuracies and root mean square bandwidth Frequency accuracy and root mean square signal duration The display of position Displays used to measure ränge Displays for surveillance Airborne displays Displays for aiming weapons Displays to indicate interference orjamming Signals used for displays Figures affecting Performance 507 References 508 Chapter 14 Performance Range Accuracy Biaserrors Random errors Resolution Resolution in ränge Resolution in azimuth angle Resolution in elevation angle Resolution in Doppler frequency Stability, the cancellation ratio 5 ] Interfering orjamming Signals Chaff or window Active jamming Deceptionjamming Tables Basic radar requirements Derived characteristics Factors for calculating ränge Resolution Accuracy Stability 524 References 525 Chapter 15 Statistics Terms Mean and expected values Variance Standard deviation Histogram and probability distribution Cumulative distribution function Percentiles and quartiles Moment generating functions Fourier transform 531

9 XIV Modern Radar Systems 15.2 Families of distributions Gaussian or normal distribution: two sided from - to Log-normal distribution Rayleigh distribution Ricean distribution Gamma distribution family: bounded on one side from 0 to Erlangian distribution Chi-squared distribution Chi distribution Negative exponential distribution Other distributions bounded on one side Weibull distribution Discrete distribution: binomial distribution Random numbers 552 References 553 Chapter 16 Transforms Conventions for the Fourier transform Some polyphase and single phase Fourier transforms Single phase cosine wave Single phase sine wave Rectangular pulse Timeshift Phase shift Examples of Fourier transforms in the complex plane Addition and subtraction Differentiation Convolution, the multiplication of Fourier transforms Cross-correlation, multiplication with complex conjugates Autocorrelation, multiplication with its own complex conjugate Energy and power Discrete Fourier transform Differences between continuous and discrete transform functions Fast transforms Summary ofproperties of the Fourier transform Tapering Gains and losses Spectral leakage or two-tone characteristics Resolution Example: von Hann and Hamming tapering functions Relationships to other transforms The z transform The use of Fourier transforms for finite impulse response filters Single-phase signal filtering Video integration in a finite impulse response filter Noncoherent moving target indicator finite impulse response filter Polyphase signal filtering 599 References 600 Appendix 16A Complete correlation 601 Appendix A Language and glossary 603 A. 1 Unified terminology 603 A. 1.1 Military words that have been avoided 603 A.1.2 Unfortunate words 603 A. 1.3 Technical words 604 A. 1.4 Words retained

10 Contents XV A. 1.5 New words 605 A. 1.6 Russian names 605 A.2 Glossary 605 A.3 Displays 614 A.3.1 Surveillance radars 615 A.3.2 Anti-aircraft (AA) artillery radars 615 A.3.3 Airborne intercept (AI) radars 615 A.3.4 Display types 615 A.3.5 Displays for showing the effects of jamming (military) 616 A.4 Symbols 617 References 617 Appendix B Tapering functions 619 B.l Conventions and normalization 619 B.l.1 Scaloping loss and worst-case processing loss 621 B. 1.2 Spectral leakage or two-tone characteristic 621 B. 1.3 Other names used for tapering functions 621 B.2 Tapering functions 622 B.2.1 Trapezoidal tapering 622 B.2.2 (1-4p ' 2 )" tapering. 626 B.2.3 Cosine to the power n tapering 629 B.2.4 Cosine on a pedestal tapering 633 B.2.5 Hamming, Blackman, and Blackman-Harris tapering 636 B.2.6 Truncated Gaussian tapering 646 B.2.7 Even Taylor tapering 649 B.3 Tapering with discrete elements 653 B.3.1 Dolph-Chebyshev tapering for a discrete 10 element System 653 B.4 Tapering or illumination functions for circular antennas 657 B.4.1 Circular (1 -Ar' 1 )" tapering 657 B.4.2 Circular truncated Gaussian tapering 660 B.4.3 Circular Taylor tapering 662 B.5 Odd tapering functions 664 B.5.1 Odd rectangular tapering 664 B.5.2 Odd triangulär tapering 667 B.5.3 Odd cosine to the power n tapering 669 B.5.4 Odd truncated Rayleigh tapering 671 B.5.5 Odd Taylor derivative tapering 673 B.5.6 Bayliss tapering 675 B.5.7 Zolotarev tapering 679 References 681 Appendix C Frequency band letters 683 List of symbols 685 About the author 693 Index 695