High resolution solutions for the multipath problem in radar

The problem of tracking radar targets in the low-angle region Where conventional monopulse radars face difficulties due to the presence of multipath waves is considered in this thesis. The emphasis of the presentation is mainly directed towards finding a new simple closed-form solution to the coherent multipath problem over a smooth surface. Another concern is to improve the performance of the three-subapertures maximum-likelihood estimator when the two received signals are in-phase or anti-phase at the centre of the array. The multipath phenomenon and its modelling for smooth and rough surfaces are discussed and simulation results obtained for different surfaces. subsequently the following are treated First. a new four-subapertures technique to improve the in-phase and anti-phase performance of the maximum likelihood estimator above is derived and simulation results are shown. Then. an improved version of this technique is introduced as a part of the new algorithm. Second. a new three-subapertures trigonometric solution to solve the coherent multipath problem is derived and demonstrated by simulation results. This new method is simpler than the maximum likelihood estimator above and very similar in its estimation accuracy. Third. the performance of the maximum entropy method is tested for the coherent multipath problem by using the three-subapertures arrangement of a linear array. Finally the performances of the above three methods and the normal phase monopulse radar are tested and compared to different surfaces when the coherent and noncoherent multipath exist together. Simulation results show that the performances of the maximum entropy method and phase monopulse are much better than the others when the target is low-tlyine over a rough surface