Institut für Hochfrequenztechnik und Elektronik Lecture Script Radar Systems Engineering by Werner Wiesbeck 16th Edition WS 2009/2010 Mail Address: Institut für Hochfrequenztechnik und Elektronik Phone: +49 (0) 721 608 25 22 Kaiserstraße 12 Secr.: +49 (0) 721 608 25 23 D-76131 Karlsruhe Fax: +49 (0) 721 69 18 65 E-Mail: [email protected] Building: Engesserstraße 5, Geb. 30.10 www.ihe.kit.edu Radar System Engineering Contents i Contents 1 The History of Radar Technology ......................................................................................... 1 2 Electromagnetic field theory & wave propagation basics................................................... 7 2.1 Fields and Waves in Free Space........................................................................................ 8 2.2 Reflection on Perfect Conducting Bodies ......................................................................... 9 2.3 Reflection on Dielectric Interfaces.................................................................................. 10 3 The Radar Equation ............................................................................................................. 13 3.1 Radar Equation for Point Targets.................................................................................... 13 3.2 Radar Equation for Extended Targets ............................................................................. 15 3.3 The Radar Horizon .......................................................................................................... 16 3.4 Bistatic Radar Equation................................................................................................... 17 4 Information Content in Radar Signals................................................................................ 19 4.1 Range............................................................................................................................... 19 4.2 Velocity ........................................................................................................................... 21 4.3 Direction (Azimuth, Elevation)....................................................................................... 21 4.4 Polarization Characteristics of the Target ....................................................................... 21 5 Resolution and Accuracy...................................................................................................... 23 5.1 Measurement Accuracy and Sine Wave Oscillations...................................................... 23 5.2 Accuracy and Range Measurement................................................................................. 24 5.3 Range Resolution of Two Neighbouring Targets............................................................ 25 5.4 Angular Resolution.......................................................................................................... 26 6 Radar Receiver Noise and Target Detection ...................................................................... 28 6.1 Thermal Noise ................................................................................................................. 28 6.2 Cosmic and Background Noise ....................................................................................... 29 6.3 Atmospheric Absorption Noise....................................................................................... 32 6.4 System Noise Temperature ............................................................................................. 33 6.5 False Alarm Rate and Probability of Detection............................................................... 35 6.6 Radar Detectors ............................................................................................................... 38 7 CW- and FM-CW Radar...................................................................................................... 41 7.1 CW Doppler Radar.......................................................................................................... 41 7.1.1 The Doppler Frequency ............................................................................................ 41 7.1.2 Quadrature Modulation ............................................................................................. 42 7.1.3 Range Measurement with CW Radar........................................................................ 43 7.2 FM CW-Radar................................................................................................................. 44 7.2.1 Range Measurement with FM CW Radar................................................................. 44 7.2.2 Range Resolution with FM CW Radar ..................................................................... 46 8 Pulse Radar............................................................................................................................ 49 Radar System Engineering Contents ii 8.1 The History of Pulse Radar ............................................................................................. 49 8.2 Transmission Types of Pulse Radar ................................................................................ 49 8.3 Simple Pulse Radar ......................................................................................................... 51 8.4 Coherent Pulse Radar ...................................................................................................... 52 8.5 MTI Radar (Moving Target Indication) .......................................................................... 54 8.5.1 MTI with Delay-Line Canceller................................................................................ 54 8.6 Filterbank Procedure ....................................................................................................... 56 8.7 Impulse Integration for Increasing the Sensitivity .......................................................... 58 8.7.1 Incoherent Integration ............................................................................................... 58 8.7.2 Examples for Incoherent Integration......................................................................... 60 8.8 Pulse Compression for Improving the Resolution .......................................................... 62 8.8.1 Compression of a frequency modulated pulse (chirp) .............................................. 62 8.8.2 Digital Pulse Compression........................................................................................ 66 8.8.3 Digital Pulse Compression with Barker Code .......................................................... 67 9 Beamforming ......................................................................................................................... 71 10 Synthetic Aperture Radar .................................................................................................. 75 10.1 Resolution Limits of Conventional Radar Devices ........................................................ 75 10.2 Procedures for Improving the Resolution....................................................................... 75 10.2.1 Range Resolution with Pulse Compression ............................................................ 75 10.2.2 Improvement of the Azimuth Resolution................................................................ 76 10.3 Basic Principle of SAR................................................................................................... 77 10.4 Theoretical Basics of SAR.............................................................................................. 79 10.5 Maximum Resolution Capability.................................................................................... 82 10.6 Analysis Procedures........................................................................................................ 82 10.7 PRF Determination ......................................................................................................... 85 11 Characteristics of Radar Targets ...................................................................................... 87 11.1 Definition of the Radar Backscattering Cross-Section................................................... 87 11.2 Fundamentals of Radar polarimetry ............................................................................... 89 11.2.1 Polarization ............................................................................................................. 89 11.2.2 Polarization Scattering Matrix ................................................................................ 90 11.3 Complex Radar Cross-Section and RCS Matrix ............................................................ 91 11.4 RCS Measurement Techniques....................................................................................... 93 11.4.1 Measurement of the Scalar Radar Cross-Section σ ................................................ 93 11.4.2 Measurement of The Complex Polarization Scattering Matrix .............................. 93 11.4.3 Calibration and Error Correction for Polarimetric RCS Measurements ................. 95 11.5 Radar Cross-Section of Simple Objects ....................................................................... 100 11.5.1 Sphere.................................................................................................................... 100 Radar System Engineering Contents iii 11.5.2 Circular Disks ....................................................................................................... 102