Research On Imaging Technology Of Chaos-coded OFDM Radar

To realize new type radar of integrative multiple functions with single form of radar is of broad perspective. For conventional radar imaging, it is almost realized by transmitting linear frequency-modulated(LFM) signal, but of which the form is simplex and the performance of covert and security is comparatively of a sort, and it is easy to be interfered by noise and other signals. To survive in the future war field, any attempt at searching a kind of single form of signal, which is to realize communication and new type wideband radar with integrative multiple functions, has been made by more and more country. In this paper, a series of studies will be done for imaging technology of radar with orthogonal frequency-division multiplexing signal based on chaotic code(COFDM).Firstly, Peak-to-Mean Envelope Power Ratio(PMEPR) OFDM signal is introduced. Several constant chaotic mapping sequences are presented, and based of which the coded OFDM signal model is built. With the different ways of modulation, such as identical sequence(IS) and non identical sequence(NIS), of phase-coded sub-carriers, the ambiguity and autocorrelation function of the COFDM signal with single pulse and pulse trains are derived in detail to analyze its properties and then the impact of the signal’s parameters, such as amplitude and phase modulation, on the main lobe width and side lobe level is discussed, which provides the foundation of parameter optimization of signal and pulse compression output of radar.Secondly, method of pulse compression of COFDM radar is analyzed. The high resolution range profile(HRRP) of COFDM signal is derived and the good performance is validated, which provides an approach for planar imaging of radar. Then, the complementary COFDM pulse pair is acquired by solution of optimized coding, and the side lobe level of different pulses of the transmitted signal, such as peak side lobe level(PSL) and integral side lobe level(ISL), is reduced by mutual elimination, through which way the side lobe parameters of the pulse compression is optimized. Then, by doing speed compensation on the echo, the complementary COFDM pulse pair behaves good performance on the side lobe under high speed measure precision.Finally, inverse synthetic aperture radar(ISAR) imaging technology of COFDM radar is analyzed. The theory of ISAR imaging of multi-carrier broadband signal is presented and the profile is derived.To set different coded matrix, comparing the imaging of OFDM pulse series coded by optimized complementary Bernoulli mapping sequence with COFDM pulse series. Then, combined with the conception of deception jamming, ISAR profiles of COFDM radar signal are analyzed, and it is validated that it has good performance of anti-jamming.