New Clutter Rejection Waveforms for Long-Range Radar

A frequent compromise in the design of long-range search radars has to be made between the maximum unambiguous detection range and the achievable coherent clutter rejection performance. A new class of waveforms is introduced which offers the designer a previously unavailable flexibility in arriving at radar designs with improved clutter rejection without seriously affecting the maximum unambiguous search range. The key to these new waveforms is the recognition that a class of useful N-pulse, nonrecursive, moving target indicator (MTI) canceler designs exists which only requires the radar to transmit a total of N -1 (nonuniformly spaced) pulses.     

Walker Model for Radar Sensing of Rigid Target Fields

The objective of this primarily tutorial item is to describe a general model for the observable data and the appropriate data processing involved in sensing rigid target fields with coherent radars. Any number of radars may be involved, and the scene and each radar may be in any kind of motion-with no restrictions on motion through resolution cells during the coherent processing time of the radars. The motions are assumed to be known. To some extent motion parameters can be estimated from the radar data, e.g., by adaptive parameter adjustments in the data processing; however, this subject is beyond the scope of this discussion. In large measure, the analysis in this item highlights the central conceptual result obtained by J.L. Walker as described in [1] -a major work in radar theory.     

WARLOC: A High-Power Coherent 94 GHz Radar

This paper describes the development of a high-power, coherent radar system at W-band and discusses potential applications of radars with this new capability. Previous radars in this frequency band were limited by available power-amplifier technology to about 500 W of average power; WARLOC radar represents an increase in power, by 20 times, over previous coherent radars at 94 GHz. This performance improvement is possible due to the development of a gyroklystron amplifier specifically for this and future radars in this frequency band. The gyroklystron amplifier tubes deliver 100 kW peak power and 10 kW of average power at a center frequency of approximately 94 GHz. Other novel features of this radar include the use of highly overmoded waveguides and rotary joints for the transmission of power from the final power amplifier (FPA) to the antenna, and a high-power quasi-optical duplexer. The system uses a relatively large 1.8 m diameter (580-wavelength) Cassegrain antenna, which required the development of an antenna with an rms surface accuracy of 0.0025 in, to obtain long-range detection and identification of small objects. Test data show an antenna gain of 62.5 dB, confirming that the needed surface accuracy was achieved. Two mobile shelters house the radar system, permitting relocation to various test sites. WARLOC is presently operational at the Naval Research Laboratory's Chesapeake Bay Detachment facility, Maryland. It is being employed in radar imaging of airborne and surface objects, and in the scientific study of propagation effects and atmospheric physics phenomena.     

Growler detection in sea clutter with coherent radars

Ship navigation through ice-infested waters is a problem of deep concern to the Canadian shipping and exploration industry. Conventional marine radars have difficulty detecting small pieces of glacial ice called growlers which are very hazardous to vessels if struck. In an effort to improve detection performance, X-band radar measurements were collected and analyzed to determine the characteristics of clutter and growler returns that could lead to their separability. These analyses suggested that coherent medium dwell-time processing (i.e., integration times of a fraction of a second) could provide improvement In growler detectability over conventional methods; and long dwell-time processing (i.e., integration times on the order of seconds) could provide even further improvement. We report on the performance of two new coherent, medium dwell-time detectors. A third detector which is representative of conventional marine radar serves as a basis for comparison Although significant improvement in growler detectability is achieved, the two coherent detectors still fall short of operational requirements. This leads to the development of a long dwell-time detector which provides considerably better performance. Empirical results indicate that this new detector could well satisfy stringent operational requirements     

Multifrequency Imaging of Radar Turntable Data

In recent years synthetic-aperture radars (SAR) have proven to be very useful two-dimensional imaging tools in various fields. Based on the synthetic-aperture concepts, different imaging modes are possibe with various operating characteristics. We describe a special case where circular-projection radar data are coherently processed to yield both azimuth and range resoultion. Experiments are performed using data obtained from the radar target scatter site (RAT SCAT) radar cross-section facility. Fairly good results are obtained which illustrate the versatility of coherent syntheticaperture processing of pulse-to-pulse high-range-resolution radar returns. A discrete multifrequency stepped and pulsed waveform is the basic transmitted signal from which range-Doppler images are generated. The RAT SCAT turntable facility allows interesting model targets to be illuminated from which radar images can then be computed. One such application of the processing is described.     

Fiber-optic radar calibration

A simple fiber-optic radar calibration target is described. Its operation is based on a wideband fiber, a laser transmitter that is directly modulated by the down-converted radar signal and an optical diode receiver recovering said signal. Further up-conversion having a common local oscillator with the first mixer ensures fidelity of the calibration return. Measured useful bandwidth exceeds 200 MHz and practically any radar RF frequency can be handled when suitable mixers are employed. Amplifiers can be added to the down-converted path as desired to compensate for the fiber loss. Modulation and LO sweep provide easy ways of introducing artificial fluctuations and Doppler frequencies. Particularly pulsed radars are readily tested with the proposed scheme as no restrictions are posed by the radar's TR-switch delays.     

Stability Measurement Problems and Techniques for Operational Airborne Pulse Doppler Radar

In the deployment of pulse Doppler (PD) radar, determination of phase and amplitude stability is the most difficult measurement problem. Unique requirements are placed on pulse and carrier stability so that the radar can perform in strong clutter. Because of subclutter visibility and sensitivity specifications, coherent noise, which is insignificant for noncoherent pulse radars, becomes extremely important. In solving the measurement problem, special support equipment was developed which is considered to have reached such a degree of refinement that it is probably one of the most technically advanced pieces of field test equipment supporting any operational radar. This paper discusses stability requirements, sources of instability, and the combination of techniques selected for verification of compliance of the PD radar with the stability requirements. The results of a program to develop special field support equipment to satisfy the measurement requirements are emphasized. Results of field experience and the special training required of military field personnel to enable them to effectively use this relatively complex support equipment are discussed.     

Performance Degradation of MTI Circuits Due to Amplitude Limiting

The loss in output signal-to-noise ratio (SNR) due to amplitude limiting is obtained for a radar circuit consisting of a bandpass limiter, coherent demodulator, matched filter, and moving-target-indicator (MTI) filter. The circuit is used in scanning MTI radars. The tandem connection of the limiter and coherent demodulator is a model for the saturation of the intermediate-frequency (IF) demodulator of an MTI radar. Results on special functions are used to obtain simple formulas for the loss in output SNR relative to a linear IF demodulator when the input SNR is less than -15 dB and the number of hits per 3-dB beamwidth exceeds 15.     

脉冲雷达探测中高轨道目标方法及试验

通过分析中高轨目标雷达回波信号特性,给出一种基于空间目标动力学约束的回波信号相参积累方法,介绍了信号积累模式下中高轨道目标的参数测量方法。通过对国内某型号雷达进行中高轨目标探测支路改造及相关试验,获取试验数据并对其进行分析,验证了原理的正确性和方法的可行性。     

An Experimental Radar Facility

A coherent CW superheterodyne radar system operating at frequencies of 9, 17, 35, and 70 GHz is described. The radars are installed on a free-flight range to study backscattering from wakes of hypersonic-velocity projectiles. Each radar is equipped with a focused-lens antenna oriented at an angle of approximately 45° to the flight axis. Amplitude and phase of the received signal are recorded separately. Some typical results are given to demonstrate the capabilities of the equipment.     

Control and utilization of range-dependent beampattern with waveform diverse array radars

The transmit antenna beampattern of the phased array radar is only a function of angle, limiting its ability to discriminate the targets from the same direction. Recently, the waveform diverse array radars expand the angle-dependent beampattern to an angle-time-range-dependent three-dimensional function by modulating the frequencies/time delays/phases across different transmit antenna elements. In this respect, extra Degrees-of-Freedom (DOFs) in the range domain are achieved, which opens up an innovative way to fulfil the tasks with enhanced system performance by jointly using the angle and range information. This paper summaries the developments of waveform diverse radars, including the Frequency Diverse Array (FDA), the Space-Time-Circulating-Array (STCA), and the Element-Pulse-Coding (EPC) frameworks, with emphasis on the analysis of the range-dependent beampattern from the basic properties upon how it is controlled. Moreover, the most recent advances of utilizing such a range-dependent beampattern in target detection, parameter estimation and identifiability, clutter suppression, jammer suppression and Synthetic Aperture Radar (SAR) imaging are discussed.     

Radar target classification of commercial aircraft

With the increased availability of coherent wideband radars there has been a renewed interest in radar target recognition. A large bandwidth gives high resolution in range which means target discrimination may be possible. Coherence makes cross-range resolution and radar images possible. Some of the problems of classifying high resolution range profiles (HRRPs) are examined and simple preprocessing techniques which may aid subsequent target classification are investigated. These techniques are applied to HRRP data acquired at a local airport using the Microwave Radar Division (MRD) mobile radar facility It is found that Boeing 727 and Boeing 737 aircraft can be reliably distinguished over a range of aspect angles. This augers well for future target classification studies using HRRPs     

相参雷达典型干扰信号产生及关键技术

介绍了一种基于DRFM的相参雷达典型干扰样式信号产生方法,并对其关键技术进行了研究。该干扰信号能够携带雷达发射信号的相位等细微特征信息,可以用于在实验室条件下对相参雷达进行抗干扰性能测试。     

Radar in the Soviet Union and Russia: a brief historical outline

This paper outlines the historical development of radar in the Soviet Union and Russia. Emphasis was given to only two classes of radars: surveillance radars for air defense (AD) systems; and radars for surface-to-air missile (SAM) systems.     

Analysis of array errors and a short-time processor in airbornephased array radars

Array errors are inherent in a realistic phased array radar system. The influence of array errors on the clutter degrees of freedom and the clutter subspace in an airborne phased array radar is analyzed. Based on the presented theoretic results, a method of short-time processing followed by coherent integration is proposed for clutter suppression in airborne phased array radars. It can approximate the two-dimensional optimal processor well even in the presence of array errors, clutter fluctuations and aircraft drift, with a considerable saving in computations     

Thinned spectrum ultrawideband waveforms using stepped-frequencypolyphase codes

An ultrawideband (UWB) radar can interfere with external RF sources because of the mutual occupancy of the same frequency band. A stepped-frequency polyphase code (SFPC) waveform is proposed as a generic UWB waveform whose interference with the external RF sources is significantly reduced. The subpulses of the individual stepped-frequency (SF) pulses are phase coded using small phase perturbations. This results in a waveform which places nulls at the frequency locations of the external RF sources. Because the phase perturbations are small, a mismatched filter which uses the unperturbed pulses (no phase modulation) as a reference signal results in a simple receiver design and a small mismatch loss on receive. Furthermore, the proposed methodology also has application to narrowband or wideband radars     

Null phase-shift polarization filtering for high-frequency radar

In order to effectively cancel the interference in polarization filtering, the parameters of the polarization filter should timely adapt to the variation of the polarization of the interference, which may impact the amplitude and phase of the desired signal that passes through the same polarization filter during the coherent integration time (CIT) and render the enhancement of the signal integration a failure. To avoid this, a null phase-shift polarization (NPSP) filter is proposed, which is composed of a linear polarization transformer (LPVT), a conventional single-notch polarization (SNP) filter and an amplitude/phase compensation device (A/PCD). The interference, which has polarization different from those of the desired target signal, can be suppressed completely while the target signal remains without distortion. Some applications of high-frequency (HF) radars for suppressing the radio interference are introduced. Simulation results from the experimentally derived data indicate that the improvement of the signal-to-interference ratio (SIR) can be expected to be more than 28 dB. The proposed NPSP filter is effective in HF radar or other coherent systems.     

A Systematic Approach to Blind-Speed Elimination

In radars that achieve a high subclutter visibility by coherent processing over several pulses, a serious problem appears in the form of blind Dopplers, or ?speeds,? at which target detection is impossible. Of the possible methods of eliminating these blind speeds, the most basic one that is employed when the performance requirements are high involves the use of several PRF's. These PRF's are chosen so that coverage is obtained at any Doppler with at least one PRF. The problem faced by the radar designer is to select the set of PRF's and the pulse numbers for each PRF so that the search frame time is minimized. This paper evolves a systematic method for the design of the blind-speed elimination scheme. A formalized approach is offered that shows the possible combinations of wavelength, PRF, and pulse number and the tradeoffs involved, without introducing the confusion ordinarily associated with multiparameter choices.     

Radar target classification using doppler signatures of human locomotion models

The problem of target classification for ground surveillance Doppler radars is addressed. Two sources of knowledge are presented and incorporated within the classification algorithms: 1) statistical knowledge on radar target echo features, and 2) physical knowledge, represented via the locomotion models for different targets. The statistical knowledge is represented by distribution models whose parameters are estimated using a collected database. The physical knowledge is represented by target locomotion and radar measurements models. Various concepts to incorporate these sources of knowledge are presented. These concepts are tested using real data of radar echo records, which include three target classes: one person, two persons and vehicle. A combined approach, which implements both statistical and physical prior knowledge provides the best classification performance, and it achieves a classification rate of 99% in the three-class problem in high signal-to-noise conditions.