Jammer Emission Leak And Multipath Signal Cancellation Algorithm Research

With the more and more important role that electronic war plays in the mordern wars, electronic equipments have already been the research emphases of many countries. Radar jammer which disturbs the enemy’s radar and makes it work abnormally by sending noise or deception jammings is a type of active jamming. The problem of isolation by the tranceivers will occur in the radar jammer unavoidably for the short distance of transmitting and receiving antennas which are both integrated in the jammer.Firstly, the dissertation analyzes the influences caused by echo signals to the radar jammers, then introduces the elementary features of wireless channel and generates the models of it. And it also makes a study of the frequency domain algorithm, slippage correlation algorithm and circular correlation algorithm to estimate the time invariant channels. Meanwhile, it puts forward an improved algorithm based on the circular correlation algorithm.In many circumstances, the channels which cause echo interference signals are time variant, the thesis deals with the interference signals by adaptive cancellation. The paper comes up with the structure provided with the interference noises adaptive cancellation of radar jammer, and briefly describes the principles of LMS algorithm, NLMS algorithm, RLS algorithm, Kalman filtering algorithm and the other adaptive filtering algorithms, then verifies and compares the properties of these algorithms by simulating adaptive cancellation of the narrowband interferences.Secondly, the thesis analyses and compares the narrowband and wideband adaptive cancellation, puts forwards utilizing the fractional delay filter to generate an accurate delay to make the inference signal and input signal aligned, and it will bring about a better effect of the wideband adaptive cancellation. The fractional delay filter is divided into two kinds:the stationary and the variable ones. As is well known, there are tow types digital fliters:the finite impulse response (FIR) filter and all-pass filter. The LS integral error method, windowing method, Lagrange internal method are researched in the paper. And it utilizes a symmetry-based low-complexity method to realize the variable fractional delay, the farrow structure is also used.Finally, the thesis proposes the cancellation structure of wideband adaptive cancellation by adding the fractional delay filter. It combinds the advantage of the DLMS algorithm and NLMS algorithm through considering the realization and covergence rate of the adaptive algorithm, and puts forward the DNLMS algorithm. And it’s proved to be fastly covergent and one more time throuput than LMS algorithm by simulation.