The Research On Echo Simulation And Low-angle Estimation In VHF Phased Array Radar

VHF radar has attracted a world-wide attention because of its unique advantages inanti-stealth. However, due to the wide beam-width, the beam might be reflected by theground when the radar detects low-angle targets. Since the coherent multipath signalbesides the direct one in target echo, the performance of direction of arrival in VHFradar will be decreased. In order to improve the estimation accuracy of the elevation andazimuth angle, this dissertation focuses on the related issues of low-angle targetsdetection in VHF radar, especially on the subspace-based low-angle estimationalgorithm, and then an elevation super-resolution method based on azimuthbeam-forming is proposed. This method will be more suitable for low elevationestimation in VHF radar by taking the advantages of element-space and beam-spaceMUSIC algorithm. The proposed method achieves higher estimation accuracy andlower complexity. The details are summarized as follows.1. The echo model of moving target in the case of multipath is constructed. Theecho model of moving target is analyzed. The model of the flat-earth and thespherical-earth reflection is established, according to the inducement of multipathreflection phenomenon. The factors affecting the reflection coefficient is analyzed,which includes the polarization mode, surface roughness, curvature of earth, etc. Toestimate the target parameter, the Range-Doppler algorithm is processed, and theMATLB software is compiled ultimately.2. The method based on beam split for measuring the altitude is researched. Usingthe certain phase relationship among the split beams of different antennas, the blindareas of angle measurement are complemented for each other, which make the elevationof target obtained. The effects on the angle measurement accuracy caused by the heightof antenna, element spacing, elevation angle of target, SNR and especially theamplitude of reflection coefficient amplitude are analyzed. The results shows that themeasurement accuracy of algorithm is related to the prior information such as thesurface reflection coefficient, polarization mode, etc.3. The low-angle estimation method based on subspace in VHF radar is researched.The theories of generalized MUSIC algorithm and decorrelation method which containsmatrix reconstruction algorithm, spatial smoothing algorithm and Toeplitz algorithm areintroduced. The performance of each decorrelation algorithm is simulated. In addition,the traditional2D MUSIC algorithm,2D beam-space MUSIC algorithm and2D spatialsmoothing algorithm are researched. According to the shortages of traditionalsuper-resolution methods used in VHF radar with strongly correlated signals, a novelmethod which proceed beam forming firstly in azimuth dimension and then estimate theelevation of target through MUSIC algorithm in elevation dimension is proposed. Simulation results and analysis are carried out to compare the performance of the threetypes of algorithm, such as spatial spectrum, the probability of successful resolution,RMSE of the DOA estimation and computational complexity. The proposed methodachieves higher estimation accuracy and further reduction of the computationcomplexity.