Research On Low-altitude Target Detection And Wideband Radar Signal Detection

Low-altitude flying targets are difficult to detect and track, and this is one of the four great threats propelling radar development. Research on detecting and tracking of low-altitude targets is of great significance to counter low-altitude air defence penetration, but up to now, this problem has not been effectively resolved.Wideband radar holds many merits, and it can enhance the low-altitude targets detecting and tracking performance. Wideband radar detection theory is still not built up, the performance of current wideband detection strategies needs to be improved, and scholars still pay no attention to moving target detection with echoes migration through resolution cells during CPI. Based on the support of the General Armament Department fund project, this dissertation formulates our study from low-altitude problem to wideband radar detection theory.The main results are as follows:1. Two new technologies for low-altitutde detection and tracking are investigated. Based on the analysis of difficult problems of low-altitude detection, we put forward frequency diversity weighting accumulation detection technology to resist multipath effect, and the detection performance is improved significantly. And then, we propose and testify a new low-angle altitude measurement method using wideband frequency scan.2. Echo characteristics of wideband radar are studied. Using the field sampled data, we study the characteristics of airborne wideband radar target echoes. From the angle of clutter generation mechanism, we also research on the time-variant and nonstationary properties of clutter cells. In this part, the amplitude distribution model, power spectrum model and statistical characteristic research methods for the wideband radar clutter are also been discussed. At last, the novel test research results are presented.3. Detection performance of wideband radar is researched on. The relationship between signal bandwidth and target echo power, clutter echo power and noise power has been analysed. Target echo energy distribution functions for wideband radar and narrowband radar are researched. And from this foundation, based on the matched filter, we compared the wideband radar detector with the narrowband radar detector, and discussed the performance improvement of the wideband radar detector.4. Wideband single pulse detectors are studied in detail. Single pulse detection structure for wideband radar is presented. The appication of the conventional detectors, such as M/N detector and norm square accumulated detector, is discussed. For wideband LFM signal, we put forward the Radon-Wigner transformation method. The derivative scattering points produced by this method can provide detection gain. SSD-GLRT detector based on the spatially scattering density assumption is researched on. And then, based on the assumption that wideband single pulse echo is a pulse train with the random amplitude-phase-time delay, we propose the modified RPPT detection method. Scattering-points windowed GLRT detection method is also proposed, and its performance is optimum relatively. At last, the optimum detection strategy for exponential distributed scattering-points of extended target is deduced out. This optimum strategy testifies the better performance of scattering-points windowed GLRT detector.5. Wideband multiple pulses detectors are studied in detail. The moving target echoes of wideband radar maybe migrate through range resolution cells bewteen two pulses duing one CPI. This makes the condition of conventional MTD can not still exist. Wideband MTD should be implemented after aligning the different periodic range cell trace of the dopper signal. Wideband MTD based on fast-time frequency domain alignment is proposed. By the cost of less computational burden increments, this method can implement wideband MTD, but SNR condition is needed. Wideband MTD based on Coherent-Radon transformation is researched on. This method is optimum for range-cell trace alignment of doppler signal, but its computational cost is too high. Based on the prior target doppler analysis, wideband MTD based on local Coherent-Radon transformation is then put forward. This is a fast computation method of the Coherent-Radon transformation method. It can implement coherent accumulation detector for the wideband target with less computational burden increments.