Study On SAR/GMTI Technology For Multi-phase Centre Receive System

In 1971, R.Keith.Raney first presented influence of slow ground moving target on quality of image formed by the synthetic aperture radar (SAR) with single antenna in his paper. During the last thirty years, scholars from different countries carried out various studies on ground moving target detection in different field. However, the essentiality to integrate the SAR with ground moving target indication (GMTI) function was not well accepted until the beginning of 1991 when US Airforce demonstrated the excellent performance of prototype of E8A battlefield reconnaissance radar JSTARS in Gulf war. Since then, domestic universities and research institutions had advance study on GMTI for different projects and made some achievements. Since the research on SAR/GMTI depends largely on practice, the theoretical results shall be proven with data obtained in the field test. In the past, there was no such kind of radar system in China. Many researches were based on simulated data, or data from foreign countries, such as Multi-Channel Airborne Radar Measurements (MCARM) from the United States. Therefore, the further study on GMTI was limited by the actual situation. In recent years, with advanced research on various SAR systems, GMTI has been required to be an essential function of them. So researchers realized that GMTI shall be put into field use. East China Research Institute of Electronic Engineering (ECRIEE) developed a new multi-mode SAR/GMTI battlefield reconnaissance radar which was firstly tested in China, large amount of data were acquired with the multi-channel SAR/GMTI multi-mode battlefield reconnaissance radar. The research work of this paper is mainly based on the data, the main contents of study are summarized as follows.Chapter 1 gives the brief introduction. It discusses and summarizes the general situation of SAR/GMTI techniques developed in the world, putting forward the basic problem of ground moving target detection. The main contents, structure and creativity of this paper are also presented.Chapter 2 describes different GMTI processing methods for multi-channel receiving system, such as DPCA, ADPCA, ATI, CSI and STAP. By comparing their advantages and disadvantages, the applicability is analyzed for each method. After deducing the minimum detectable velocity (MDV) of double-channel receivers system in detail, it comes to the conclusion that MDV of double-channel receivers system is one-fourth of single channel receiver system.Chapter 3 presents the studies on the signal processing technologies for three-channel airborne radar in wide-area GMTI and simultaneous SAR/GMTI modes. The processing methods such as calculation of optimum weight of ADPCA, phase compensate and clutter suppression between channels, signal coherent accumulation, Doppler estimation of moving target, CFAR detection, moving target location, radial velocity estimation and performance analysis are discussed in detail. Some processing methods are substituted for simplifying approximate expressions. Data pre-processing, MTD and unwrapping azimuth ambiguity of moving target are used to obtain better clutter suppression and locate moving target accuracy. An ordered statistics-based VI-CFAR detector is also used to remove the influence of non-uniform distribution and different Doppler frequency on space residual clutter. Computer simulation result shows that the moving target detection method presented in this chapter is valid.Chapter 4 contains approaches to establish a hardware-in-loop simulation test system for multi-channel SAR/GMTI. After deducing simulation echo model, the author uses point-to-point overlay and two dimensional convolution to simulate point target and regional target in the hardware-in-loop platform. By analyzing the real data collecting from the hardware-in-loop simulation test system, the contents, procedures, methods and results are given to evaluate the performance for new SAR/GMTI system in laboratory.Chapter 5 gives an in-depth study on channels I/Q calibration, equalizing amplitude and phase imbalance between channels. By analyzing different image frequency on narrowband frequency signal and linear frequency modulated (LFM) signal, the paper presents a new approach called"Time-domain division"to solve the image frequency of LFM. Based on the view of point, the author gives three new methods for processing and evaluating wideband image frequency, namely Amplitude Immovability Calibration, Image Removal and Normalized Calibration. To deal with the disadvantage of amplitude and phase imbalance between channels operating in GMTI processing, the paper puts forward a complete solving scheme for a multi-channel SAR/GMTI system. By self-calibrating T/R modules in active phased-array antenna and channels equalizing, the author got a good result in the processing of live data. Channels equalization technology presented in this chapter is very useful for wideband signal system, which is in the area such as InSAR, multi-band SAR, multi-polarization SAR and wide-swath SAR.Chapter 6 focuses on processing live data collected by three-channel SAR/GMTI system. To avoid strong reflect point target impact on estimate of Doppler centre frequency, an improved method based on energy peak value is given. According to different scenarios sub-image correlation and contrast maximization is combined for Doppler frequency modulation rate estimate in real-time processing. An improved Range-Doppler algorithm for real-time strip mode imaging. By increasing dwell pulses for each scan beam position high resolution in spotlight mode imaging is achieved. Spotlight imaging to strip imaging are realized with de-chirp demodulation function. A lot of processing results are given in simultaneous SAR/GMTI mode, such as sub-images of three channel, residual sub-images after channels cancellation. Method and rule of moving target plot filter, plot coherence and precise parameter estimation are discussed. The performances of cooperative moving targets are analyzed. Uncooperative moving targets added to SAR image are illustrated by processing some typical scenarios, such as countryside road, expressway and railroad. After space phase difference compensated in wide-area GMTI mode, it can be observed that△-beam forming a notch filter corresponding to peak energy point ofΣ-beam (or close to ) from the ADPCA processing result of cooperative target. So energy superpose forΣ-beam and energy is counteracted for△-beam. ADPCA processing principle is used to reach the purpose of desirable clutter suppression and forming continuous target tracks after detection.In the conclusion of this paper, the main contents and results are comprehensively summarized. Some questions associated with this paper are given as well, which deserves to be studied deeply in the future.