Study On Waveform Design And Subarray Division Methods Of Airborne DDMA-MIMO Radar

The airborne DDMA-MIMO radar transmits Doppler Frequency Division Multiple Access(DDMA)signals.It uses Fourier orthogonal basis as the inter-pulse modulation weighting of the transmitted signals of different array elements,that is,the transmission phase changes with the array element number and pulse number.It is equivalent to adding a Doppler frequency to each array element during transmission,and the Doppler filter bank can be used to separate the transmission signals of different array elements during reception.Although the slow time MIMO radar using DDMA signals has the advantages of simple structure,high echo correlation,and high bandwidth utilization.However,under the premise that the pulse repetition frequency of the unambiguity distance is unchanged,its Doppler non-ambiguity interval is smaller,and the high-speed target with a large Doppler frequency shift is easily mixed with the clutter of other array elements.As a result of incorrect separation,more blind speeds occur.Designing more complex DDMA waveforms can alleviate the Doppler ambiguity problem and reduce the blind speed of target detection,so it is a practical research direction.In addition,there are often many antenna array elements in the actual radar.It is impossible to assign different DDMA waveforms to each array element,and there is no need to perform fully adaptive processing on the echoes received by all array elements.Therefore,research on dimensionality reduction methods must be carried out in a targeted manner to reduce the degree of freedom of the system at the transmitting and receiving ends.Aiming at the problem that DDMA signals can easily cause Doppler ambiguity and lead to blind speed,this thesis proposes two optimal design methods for phase-jitter DDMA waveforms: angle search method and random screening method.Then,the phase jitter method is used to improve the frequency jitter DDMA waveform performance,that is,frequency jitter combined with the phase jitter method,which significantly reduces the blind speed of high-speed moving target detection.Aiming at the problem of high complexity of transmit coding and all-space-time-code(waveform)adaptive processing that occurs when there are many transmit and receive array elements in airborne DDMA-MIMO radar,this thesis improves the random extraction and division method through repeated experiments.By comparing the range Doppler diagrams,improvement factors and spatial response of different sub-arrays,the optimal division method of sub-array DDMA waveform and sub-array jitter DDMA waveform is obtained.The specific content of the thesis is as follows:1.Research on airborne DDMA-MIMO radar modeling and clutter suppression methods.First,the clutter model of the airborne DDMA-MIMO radar is established,and the echo processing flow of the DDMA signal in the time domain and frequency domain is studied under this model.Then,study the characteristics of the emission pattern of the airborne DDMA-MIMO radar.Finally,the full space-time-code(waveform)adaptive signal processing method and the reduced-dimensional space-time-code(waveform)adaptive signal processing method for airborne DDMA-MIMO radar are studied.2.Research the Doppler ambiguity characteristics and waveform design methods of DDMA signals.First,the Doppler ambiguity characteristics of DDMA waveform,frequency jitter DDMA waveform,and phase jitter DDMA waveform are studied,and the DDMA signal ambiguity function and the target aliasing formula of the three waveforms are derived,and the jitter waveform can alleviate the Doppler ambiguity problem.s reason.Then,two optimal design methods for phase jitter DDMA waveforms are proposed: angle search method and random selection method.Finally,the frequency jitter combined with the phase jitter DDMA waveform is studied,and the principle of the phase jitter method is used to improve the frequency jitter method.3.Research the sub-array division method of airborne DDMA-MIMO radar.Firstly,the dimensionality reduction principle of the airborne DDMA-MIMO radar transmitter,the Doppler ambiguity characteristics of the sub-array DDMA orthogonal waveform and the characteristics of the emission pattern are analyzed.Then,on this basis,five methods and principles of sub-array division of the DDMA receiving array are studied,and the random extraction division method is improved.Finally,by comparing the range Doppler diagram,improvement factor,and spatial response after different division methods,the optimal sub-array division method in the two cases of ordinary DDMA waveform and jittered DDMA waveform is obtained.