Clutter Modeling And Clutter Suppression For Airborne DDMA MIMO Radar

Over the past decade,Multiple-input multiple-output(MIMO)radar as a new radar system has been receiving extensive attention from researchers.It is generally believed that using the separable characteristics of MIMO radar transmission waveforms can provide more system degrees of freedom and a longer equivalent phase center baseline than single-input multiple-output(SIMO)radars,and is expected to get better results in target detection,resolution and parameter estimation.However,the traditional MIMO radar needs to be equipped with an independent waveform generator for each transmitting array element,which results in higher cost.In addition,the orthogonal waveform will also destroy the echo correlation of the clutter,so that the clutter suppression cannot be performed by the degree of freedom of transmission.Slow-time MIMO radar is expected to overcome the above two problems,and may be used in airborne radar.It is based on the conventional SIMO radar,and the orthogonality between the waveforms is realized between the pulses through the phase shifter of the transmitter.But from the basic theory to the application,including the ambiguity function,clutter suppression method and the problems caused by Doppler ambiguity,further research is needed.Therefore,it is of great significance to carry out research on airborne slow time MIMO radar.In this paper,by analyzing the typical slow-time MIMO Doppler Division Multiple Access(DDMA)signal,the target and clutter model under the DDMA waveform are established.Starting from the output of the matched filter,the ambiguity function of the DDMA waveform is deduced,the resolution ability of the DDMA waveform to targets with different distances and different speeds is analyzed,and the problems of target blind speeds and Doppler ambiguities are analyzed.Aiming at the blind speeds problem caused by clutter Doppler ambiguities,the principle of frequency-dithered DDMA and phase dithered DDMA to eliminate the blind speeds is studied.On this basis,a new method to solve the target blind speeds is given by improvement.For the problem of clutter suppression for DDMA MIMO radar,the Factored Approach(FA)and the Extended Factored Approach(EFA)method for Space-Time Adaptive Processing(STAP)of DDMA waveforms are studied,and improve the conventional SIMO radar array element pulse domain and array element Doppler domain STAP method,apply it to DDMA MIMO radar.The following is the main content of the paper:1.The echo model and the time-varying characteristics of the MIMO radar's pattern under the DDMA waveform are studied.The target and clutter echo model of the DDMA waveform are established,and the pattern function of the DDMA waveform varying with the pulse is deduced under this model.Finally,the characteristics of the radar pattern are analyzed by simulation.2.The method of DDMA signal to eliminate the target blind speeds and Doppler ambiguities is studied.First,the ambiguity function of the DDMA waveform is derived,and the resolution ability of the DDMA waveform to different distances and different speeds targets is analyzed.Secondly,the existing frequency-dithered DDMA and phase dithered DDMA for eliminating blind speed are studied.A new method to solve the target blind speeds and Doppler ambiguities.This method divides the pulses in a CPI and adds different random phases or fixed phases to the pulses of different sections.The results obtained compare with the existing ones,can obtain a better minimum detectable velocity.3.The clutter suppression method of DDMA MIMO radar is studied.First,the method of clutter suppression by FA and EFA in DDMA MIMO radar is studied,and the clutter suppression performance of DDMA MIMO radar and SIMO radar is compared.Secondly,by improving the pulse field and Doppler field of conventional SIMO radar elements,the STAP method is applied to the STAP processing of the DDMA MIMO radar,and the pulse domain dimensionality reduction processing method of the DDMA MIMO radar is obtained.Finally,the effectiveness of the space-time processing method of the pulse domain and the Doppler domain of the DDMA MIMO radar is analyzed through simulation.