《电子工程师手册》学习资料（英文版）Chapter 41 Radar

Belcher. M. L. Nessmith JT. Wiltse. J C."Radar The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000

Belcher, M.L., Nessmith, J.T., Wiltse, J.C. “Radar” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000

41 Radar elvin l. belcher 41.1 Pulse Radar Georgia Tech Research Institute Overview of pulsed Radars Josh T. Nesmith Technology. Radar Perfor Georgia Tech Research Institute h.Estimation and Tracking Continuous Wave Radar James C. Wiltse CW Doppler Radar. FM/CW Radar. Interrupted Frequency- Georgia Tech Research Institute Modulated CW(IFM/CW). Applications. Summary Comments 41.1 Pulse radar Melvin L. Belcher and Josh T. Nessmith Overview of pulsed Radars Basic Concept of Pulse Radar Operation The basic operation of a pulse radar is depicted in Fig. 41. 1. The radar transmits a pulse of rF energy and then receives returns(reflections) from desired and undesired targets. Desired targets may include space, airborn and sea-and/or surface-based vehicles. They can also include the earths surface and the atmosphere, depending on the application. Undesired targets are termed clutter Clutter sources include the ground, natural and man- made objects, sea, atmospheric phenomena, and birds. Short-range/low-altitude radar operation is often con- strained by clutter since the multitude of undesired returns masks returns from targets of interest such as aircraft. The range, azimuth angle, elevation angle, and range rate can be directly measured from a return to estimate target position and velocity Signature data can be extracted by measuring the amplitude, phase, and polarization of the return Pulse radar affords a great deal of design and operational flexibility. Pulse duration and pulse rate can be tailored to specific applications to provide optimal performance. Modern computer-controlled multiple-func- tion radars exploit this capability by choosing the best waveform from a repertoire for a given operational mode and interference environment automatically. Radar Applications The breadth of pulse radar applications is summarized in Table 41. 1. Radar applications can be grouped into search, track, and signature measurement applications. Search radars are used for tracking but have relatively large range and angle errors. The search functions favor broad beam-widths and low bandwidths in order to fficiently search over a large spatial volume. As indicated in Table 41.1, search is preferably performed in the lower frequency bands. The antenna pattern is narrow in azimuth and has a cosecant pattern in elevation to provide acceptable coverage from the horizon to the zenith Tracking radars are typically characterized by a narrow beamwidth and moderate bandwidth in order to provide accurate range and angle measurements on a given target. The antenna pattern is a pencil beam with approximately the same dimensions in azimuth and elevation. Track is usually conducted at the higher frequency bands in order to minimize the beamwidth for a given antenna aperture area. After each return from a target c 2000 by CRC Press LLC

© 2000 by CRC Press LLC 41 Radar 41.1 Pulse Radar Overview of Pulsed Radars • Critical Subsystem Design and Technology • Radar Performance Prediction • Radar Waveforms • Detection and Search • Estimation and Tracking 41.2 Continuous Wave Radar CW Doppler Radar • FM/CW Radar • Interrupted Frequency￾Modulated CW (IFM/CW) • Applications • Summary Comments 41.1 Pulse Radar Melvin L. Belcher and Josh T. Nessmith Overview of Pulsed Radars Basic Concept of Pulse Radar Operation The basic operation of a pulse radar is depicted in Fig. 41.1. The radar transmits a pulse of RF energy and then receives returns (reflections) from desired and undesired targets. Desired targets may include space, airborne, and sea- and/or surface-based vehicles. They can also include the earth’s surface and the atmosphere, depending on the application. Undesired targets are termed clutter. Clutter sources include the ground, natural and man￾made objects, sea, atmospheric phenomena, and birds. Short-range/low-altitude radar operation is often con￾strained by clutter since the multitude of undesired returns masks returns from targets of interest such as aircraft. The range, azimuth angle, elevation angle, and range rate can be directly measured from a return to estimate target position and velocity. Signature data can be extracted by measuring the amplitude, phase, and polarization of the return. Pulse radar affords a great deal of design and operational flexibility. Pulse duration and pulse rate can be tailored to specific applications to provide optimal performance. Modern computer-controlled multiple-func￾tion radars exploit this capability by choosing the best waveform from a repertoire for a given operational mode and interference environment automatically. Radar Applications The breadth of pulse radar applications is summarized in Table 41.1. Radar applications can be grouped into search, track, and signature measurement applications. Search radars are used for tracking but have relatively large range and angle errors. The search functions favor broad beam-widths and low bandwidths in order to efficiently search over a large spatial volume. As indicated in Table 41.1, search is preferably performed in the lower frequency bands. The antenna pattern is narrow in azimuth and has a cosecant pattern in elevation to provide acceptable coverage from the horizon to the zenith. Tracking radars are typically characterized by a narrow beamwidth and moderate bandwidth in order to provide accurate range and angle measurements on a given target. The antenna pattern is a pencil beam with approximately the same dimensions in azimuth and elevation. Track is usually conducted at the higher frequency bands in order to minimize the beamwidth for a given antenna aperture area. After each return from a target Melvin L. Belcher Georgia Tech Research Institute Josh T. Nessmith Georgia Tech Research Institute James C. Wiltse Georgia Tech Research Institute

△,△ △△ Target Range Two-Way-Time. Delay Speed-of-Light FIGURE 41.1 Pulse radar TABLE 41.1 Radar Bands Band Over-the-horizon radar MHz Long-range search UHF Long-range surveillance MHz Long-range surveillance Long-range weather characterization Terminal air traffic control 4000-8000MHz re control Instrumentation tracking 8-12 GHz re control Air-to-air missile seeker Marine radar Airborne weather characterization 12-18GHz Short-range fire control Remote sensing 27-40GHz Remote sensing 40-75GHz Remote sensing Weapon guidance 75-110 GHz Remote sensing Weapon guidance is received, the range and angle are measured and input into a track filter. Track filtering smooths the data to refine the estimate of target position and velocity. It also predicts the target's flight path to provide range gating tenna pointing control to Signature measurement applications include remote sensing of the environment as well as the measurement of target characteristics. In some applications, synthetic aperture radar(SAR)imaging is conducted from aircraft or satellites to characterize land usage over broad areas. Moving targets that present changing aspect to the radar can be imaged from airborne or ground-based radars via inverse synthetic aperture radar(ISAR)tech- niques. As defined in the subsection"Resolution and Accuracy, " cross-range resolution improves with increasing antenna extent Sar/ISAR effectively substitutes an extended observation interval over which coherent returns are collected from different target aspect angles for a large antenna structure that would not be physically realizable in many instances. In general, characterization performance improves with increasing frequency because of the associated improvement in range, range rate, and cross-range resolution. However, phenomenological characterization support environmental remote sensing may require data collected across a broad swath of frequencies. A multiple-function phased array radar generally integrates these functions to some degree. Its design usually driven by the track function. Its operational frequency is generally a compromise between the lower e 2000 by CRC Press LLC

© 2000 by CRC Press LLC is received, the range and angle are measured and input into a track filter. Track filtering smooths the data to refine the estimate of target position and velocity. It also predicts the target’s flight path to provide range gating and antenna pointing control to the radar system. Signature measurement applications include remote sensing of the environment as well as the measurement of target characteristics. In some applications, synthetic aperture radar (SAR) imaging is conducted from aircraft or satellites to characterize land usage over broad areas. Moving targets that present changing aspect to the radar can be imaged from airborne or ground-based radars via inverse synthetic aperture radar (ISAR) tech￾niques.As defined in the subsection “Resolution and Accuracy,” cross-range resolution improves with increasing antenna extent. SAR/ISAR effectively substitutes an extended observation interval over which coherent returns are collected from different target aspect angles for a large antenna structure that would not be physically realizable in many instances. In general, characterization performance improves with increasing frequency because of the associated improvement in range, range rate, and cross-range resolution. However, phenomenological characterization to support environmental remote sensing may require data collected across a broad swath of frequencies. A multiple-function phased array radar generally integrates these functions to some degree. Its design is usually driven by the track function. Its operational frequency is generally a compromise between the lower FIGURE 41.1 Pulse radar. TABLE 41.1 Radar Bands Band Frequency Range Principal Applications HF 3–30 MHz Over-the-horizon radar VHF 30–300 MHz Long-range search UHF 300–1000 MHz Long-range surveillance L 1000–2000 MHz Long-range surveillance S 2000–4000 MHz Surveillance Long-range weather characterization Terminal air traffic control C 4000–8000 MHz Fire control Instrumentation tracking X 8–12 GHz Fire control Air-to-air missile seeker Marine radar Airborne weather characterization Ku 12–18 GHz Short-range fire control Remote sensing Ka 27–40 GHz Remote sensing Weapon guidance V 40–75 GHz Remote sensing Weapon guidance W 75–110 GHz Remote sensing Weapon guidance

ANALOG DIGITAL TRANSMITTER TIMING DAT CONTROL PROCESSOR EXCITER RECEIVER PROCESSOR DISPLAYS ANTENNA ANTENNA BEAMPOI SIGNAL FLOW CONTROL FLOW FIGURE 41.2 Radar system architecture. frequency of the search radar and the higher frequency desired for the tracking radar. The degree of signature measurement implemented to support such functions as noncooperative target identification depends on the resolution capability of the radar as well as the operational user requirements. Multiple-function radar desig represents a compromise among these different requirements. However, implementation constraints, multiple- get handling requirements, and reaction time requirements often dictate the use of phased array radar systems integrating search, track, and characterization functions. Critical Subsystem Design and Technology The major subsystems making up a pulse radar system are depicted in Fig. 41. 2. The associated interaction between function and technology is su ed in this subsection Antenna The radar antenna function is to first provide spatial directivity to the transmitted EM wave and then to intercept the scattering of that wave from a target. Most radar antennas may be categorized as mechanically scanning or electronically scanning. Mechanically scanned reflector antennas are used in applications where rapid beam scanning is not required. Electronic scanning antennas include phased arrays and frequency scanned antennas Phased array beams can be steered to any point in their field-of-view, typically within 10 to 100 us, depending desirable in multiple function radars since they can interleave search operations with multiple target tracks c on the latency of the beam steering subsystem and the switching time of the phase shifters. Phased arrays ar There is a Fourier transform relationship between the antenna illumination function and the far-field antenna pattern. Hence, tapering the illumination to concentrate power near the center of the antenna suppresses sidelobes while reducing the effective antenna aperture area. The phase and amplitude control of the antenna illumination determines the achievable sidelobe suppression and angle measurement accuracy Perturbations in the illumination due to the mechanical and electrical sources distort the illumination function and constrain performance in these areas. Mechanical illumination error sources include antenna ape deformation due to sag and thermal effects as well as manufacturing defects. Electrical illumination error is of particular concern in phased arrays where sources include beam steering computational error and phase after quantization. Control of both the mechanical and electrical perturbation errors is the key to both low sidelobes and highly accurate angle measurements. Control denotes that either tolerances are closely held and maintained or that there must be some means for monitoring and correction. Phased arrays are attractive for low sidelobe applications since they can provide element-level phase and amplitude control c2000 by CRC Press LLC

© 2000 by CRC Press LLC frequency of the search radar and the higher frequency desired for the tracking radar. The degree of signature measurement implemented to support such functions as noncooperative target identification depends on the resolution capability of the radar as well as the operational user requirements. Multiple-function radar design represents a compromise among these different requirements. However, implementation constraints, multiple￾target handling requirements, and reaction time requirements often dictate the use of phased array radar systems integrating search, track, and characterization functions. Critical Subsystem Design and Technology The major subsystems making up a pulse radar system are depicted in Fig. 41.2. The associated interaction between function and technology is summarized in this subsection. Antenna The radar antenna function is to first provide spatial directivity to the transmitted EM wave and then to intercept the scattering of that wave from a target. Most radar antennas may be categorized as mechanically scanning or electronically scanning. Mechanically scanned reflector antennas are used in applications where rapid beam scanning is not required. Electronic scanning antennas include phased arrays and frequency scanned antennas. Phased array beams can be steered to any point in their field-of-view, typically within 10 to 100 ms, depending on the latency of the beam steering subsystem and the switching time of the phase shifters. Phased arrays are desirable in multiple function radars since they can interleave search operations with multiple target tracks. There is a Fourier transform relationship between the antenna illumination function and the far-field antenna pattern. Hence, tapering the illumination to concentrate power near the center of the antenna suppresses sidelobes while reducing the effective antenna aperture area. The phase and amplitude control of the antenna illumination determines the achievable sidelobe suppression and angle measurement accuracy. Perturbations in the illumination due to the mechanical and electrical sources distort the illumination function and constrain performance in these areas. Mechanical illumination error sources include antenna shape deformation due to sag and thermal effects as well as manufacturing defects. Electrical illumination error is of particular concern in phased arrays where sources include beam steering computational error and phase shifter quantization. Control of both the mechanical and electrical perturbation errors is the key to both low sidelobes and highly accurate angle measurements. Control denotes that either tolerances are closely held and maintained or that there must be some means for monitoring and correction. Phased arrays are attractive for low sidelobe applications since they can provide element-level phase and amplitude control. FIGURE 41.2 Radar system architecture

TABLE 41.2 Pulse Radar Transmitter Techne Mode of Maximum Demonstrated Peak/ Typical Typical Technology Operation Frequency(GHz) Average Power(kw) Gain Thermionic Magnetron Oscillate 95 Mw/500 W @X-band n/a Fixed-10%6 4 kW/400 W @X-band 40-60 dB Oct wave tube(Tw Ring-loop TWT kw/200 w @x-band 40-60 dB 5-15%6 Coupled-cavity TWT Amplif 100 kw/25 kw @X-band 40-60 dB 5-15% Extended interaction Oscillator kw/10 W@95 GHz n/a 0.2%(elec.) oscillator(EIO) Extended interaction Klystron(ElK) lkw/0W@95GHz40-50dB0.5-1% 50 kw/5 kw X-band 30-60 dB 0.1-2%(inst) -10%(mech.) Crossed-field 500 kw/1 kw @X-band 10-20 dB 5-15% amplifier(CFA) Silicon br Amplifier 300W/30W@IGHz5-10dB10-25% Amplifier 5-10dB5-20% Impatt diode Oscillator 30 W/10 w@ X-band Source: Tracy V. Wallace, Georgia Tech Research Institute, Atlanta, Georgia. Transmitter The transmitter function is to amplify waveforms to a power level sufficient for target detection and estimation. There is a general trend away from tube-based t tters toward solid-state transmitters. In particular, solid state transmit/receive modules appear attractive for constructing phased array radar systems. In this case, each radiating element is driven by a module that contains a solid-state transmitter, phase shifter, low-noise amplifier, and associated control components. Active arrays built from such modules appear to offer significant reliability advantages over radar systems driven from a single transmitter. However, microwave tube technology continue offer substantial advantages in power output over solid-state technology. Transmitter technologies are summarized in Table 41.2 Receiver and Exciter This subsystem contains the precision timing and frequency reference source or sources used to derive the master oscillator and local oscillator reference frequencies. These reference frequencies are used to downconvert received signals in a multiple-stage superheterodyne architecture to accommodate signal amplification and nterference rejection. The receiver front end is typically protected from overload during transmission through the combination of a circulator and a transmit/receive switch The exciter generates the waveforms for subsequent transmission. As in signal processing, the trend is toward programmable digital signal synthesis because of the associated flexibility and performance stabilit Signal and data processing Digital processing is generally divided between two processing subsystems, i.e., signals and data, according the algorithm structure and throughput demands. Signal processing includes pulse compression, Doppler filtering, and detection threshold estimation and testing Data processing includes track filtering, user interface support, and such specialized functions as electronic counter-counter measures(ECCM)and built-in test(BIT) as well as the resource management process required to control the radar system. The signal processor is often optimized to perform the repetitive complex multiply-and-add operations associated with the fast Fourier transform(FFT). FFT processing is used for implementing pulse compression via fast convolution and for Doppler filtering. Fast convolution consists of taking the FFT of the digitized receiver output, multiplying it by the stored FFT of the desired filter function, and then taking the inverse FFT e 2000 by CRC Press LLC

© 2000 by CRC Press LLC Transmitter The transmitter function is to amplify waveforms to a power level sufficient for target detection and estimation. There is a general trend away from tube-based transmitters toward solid-state transmitters. In particular, solid￾state transmit/receive modules appear attractive for constructing phased array radar systems. In this case, each radiating element is driven by a module that contains a solid-state transmitter, phase shifter, low-noise amplifier, and associated control components. Active arrays built from such modules appear to offer significant reliability advantages over radar systems driven from a single transmitter. However, microwave tube technology continues to offer substantial advantages in power output over solid-state technology. Transmitter technologies are summarized in Table 41.2. Receiver and Exciter This subsystem contains the precision timing and frequency reference source or sources used to derive the master oscillator and local oscillator reference frequencies. These reference frequencies are used to downconvert received signals in a multiple-stage superheterodyne architecture to accommodate signal amplification and interference rejection. The receiver front end is typically protected from overload during transmission through the combination of a circulator and a transmit/receive switch. The exciter generates the waveforms for subsequent transmission. As in signal processing, the trend is toward programmable digital signal synthesis because of the associated flexibility and performance stability. Signal and Data Processing Digital processing is generally divided between two processing subsystems, i.e., signals and data, according to the algorithm structure and throughput demands. Signal processing includes pulse compression, Doppler filtering, and detection threshold estimation and testing. Data processing includes track filtering, user interface support, and such specialized functions as electronic counter-counter measures (ECCM) and built-in test (BIT), as well as the resource management process required to control the radar system. The signal processor is often optimized to perform the repetitive complex multiply-and-add operations associated with the fast Fourier transform (FFT). FFT processing is used for implementing pulse compression via fast convolution and for Doppler filtering. Fast convolution consists of taking the FFT of the digitized receiver output, multiplying it by the stored FFT of the desired filter function, and then taking the inverse FFT TABLE 41.2 Pulse Radar Transmitter Technology Mode of Maximum Demonstrated Peak/ Typical Typical Technology Operation Frequency (GHz) Average Power (kW) Gain Bandwidth Thermionic Magnetron Oscillator 95 1 MW/500 W @ X-band n/a Fixed–10% Helix traveling Amplifier 95 4 kW/400 W @ X-band 40–60 dB Octave/multioctave wave tube (TWT) Ring-loop TWT Amplifier 18 8 kW/200 W @ X-band 40–60 dB 5–15% Coupled-cavity TWT Amplifier 95 100 kW/25 kW @ X-band 40–60 dB 5–15% Extended interaction Oscillator 220 1 kW/10 W @ 95 GHz n/a 0.2% (elec.) oscillator (EIO) 4% (mech.) Extended interaction Klystron (EIK) Amplifier 140 1 kW/10 W @ 95 GHz 40–50 dB 0.5–1% Klystron Amplifier 35 50 kW/5 kW @ X-band 30–60 dB 0.1–2% (inst.) 1–10% (mech.) Crossed-field Amplifier 18 500 kW/1 kW @ X-band 10–20 dB 5–15% amplifier (CFA) Solid state Silicon BJT Amplifier 5 300 W/30 W @1 GHz 5–10 dB 10–25% GaAs FET Amplifier 30 15 W/5 W @ X-band 5–10 dB 5–20% Impatt diode Oscillator 140 30 W/10 W @ X-band n/a Fixed–5% Source: Tracy V. Wallace, Georgia Tech Research Institute, Atlanta, Georgia