Research On Performance Of Anti-jamming For OFDM Coded Radar Signal

With the development of electronic countermeasure technology,electromagnetic countermeasure environment is becoming more and more complex.The development of radar technology requires not only high precision measurement capability and target resolution,but also low interception and anti-jamming capability.Therefore,the research on waveform modulation has gradually become a hot spot.Coded radar signal based on Orthogonal Frequency Division Multiplexing(OFDM)is a kind of radar signal with complex intra-pulse structure,multi-dimensional modulation mode and flexible waveform parameters.It has large time-bandwidth product,large pulse pressure gain,excellent range-velocity resolution and high measurement accuracy.As a new type of radar signal,reconnaissance and Research on it is a frontier topic in radar countermeasure.Therefore,this paper will focus on OFDM coded and modulated radar signal from many aspects.The details are as follows:Firstly,the basic analysis tools of waveform design theory are introduced,and the effects of various parameters on the performance of radar system are described.Several typical broadband radar signals are analyzed in detail from time domain,frequency domain and pulse compression performance.Secondly,because Phase Coded(PC)is one of the most commonly used modulation modes in OFDM,this paper introduces carrier frequency coding based on traditional modulation mode,and obtains an OFDM radar signal based on Chaotic FM-PM(CFP).Chaotic sequence is used to code and modulate OFDM from time domain and frequency domain respectively.Based on the ambiguity function,pulse compression performance and low probability of Interception(LPI)performance,the OFDM radar signals under several other conventional modulation modes are compared and analyzed.In the evaluation of low interception performance,for the modern interception mode,by introducing cyclic accumulation U factor as jammer gain into the interception factor,the relationship between waveform parameters and evaluation factors is established,and the factor is redefined to quantitatively evaluate the low interception performance of radar signals.Finally,this paper studies the anti-jamming performance of OFDM coded radar signals from three different jamming modes:suppressed jamming,deceptive jamming and intermittent sampling and forwarding jamming.For suppressed jamming,the idea of frequency sparsity is applied to OFDM coding system,and an anti-active suppressed jamming method based on frequency sparsity of OFDM coding radar is designed.The results show that this method can make OFDM coded radar resist suppressed jamming effectively.For range deception jamming,because of the orthogonality of chaotic sequence,the inter-pulse subcarrier frequency agility and inter-pulse coding agility of OFDM coded radar signal can be easily countered.Then,a new type of wideband radar jamming,Interrupted-Sampling Repeater Jamming(ISRJ),is used to simulate and analyze the jamming of OFDM coded signals.It is found that even if the modulation mode of OFDM coded radar is changeable and the intra-pulse structure is complex,it can not resist the intermittent sampling and forwarding jamming.Therefore,in view of the intermittent and discontinuous sampling characteristics of jammers for large bandwidth signals,this paper proposes an anti-intermittent sampling and forwarding jamming method based on OFDM coded radar.By using the orthogonality between subcarriers,this method can obtain the effect of mutual shielding,and can easily suppress the intermittent sampling and forwarding interference.