Research And Implementation Of LFM Pulse Radar Forward-type Interference Countermeasure Algorithm

Repeater jamming signal generated by a digital radio frequency memory(DRFM)jammer could achieve large coherent processing gain.The rejection of the repeater jamming has become a unavoidable problem to overcome for the Linear Frequency Modulation(LFM)pulse radar.The thesis focuses on rejection of repeater jamming for LFM radar.The main works are as follows:Firstly,the target echo and the range deception jamming are modeled for LFM pulse radar.A range deception jamming rejection algorithm is designed by stretch processing the received signal in a Coherent Process Internal(CPI).The target echo and the range deception jamming is separated in the frequency domain by stretch processing,and the stretch processed signal is then filtered to reject the jamming.Simulation results are given to show the validity of the algorithm.The method is implemented on the hardware platform based on DSP+FPGA.Secondly,utilizing the characteristic of phase quantization of the DRFM jammer,a method based on signal separation and a statistic named mean variance of phase statistical times(MVPST)to discriminate repeater jamming from the true target echo is introduced.The target and jamming are separated individually by Moving Target Detection,and then Fractional Fourier Transform(FRFT)is employed to reduce the noise of the separated target and jamming.The statistic MVPST is calculated for the noise reduced signal,and the repeater jamming is identified by using MVPST.Simulation result shows that the proposed method can separate and identify the jamming in the low SNR situation with a high probability.Thirdly,based on the fact that the pulse repeated by the jammer lags kdelay Pulse Repetition Intervals(PRIs)relative to the pulse transmitted by the radar,a DRFM jamming suppression algorithm based on multi-channel processing and inter-pulse phase cubing-modulation is designed.Multi-channel processing is utilized to estimate the lag PRI kdelay.The coefficient of cubing-modulation is adjusted according to the estimated kdelay,then the FRFT and masking processing is used to suppress the repeater jamming.Simulation result is demonstrated to show the efficiency of the method.