Study On Clutter Suppression Method For Airborne FDA-MIMO Radar

As the detection power of airborne early warning radar increases,the longer the detection range,the more serious the problem of range ambiguity.Especially the short-range strong clutter will lead to the deterioration of the detection performance of the long-range target.At this time,the range ambiguous clutter becomes the key problem that restricts the target detection.Frequency Diversity Array(FDA),as a new waveform diversity radar system,generates a range-dimensional degree of freedom by introducing tiny frequency increments between transmitting array elements,and provides a new idea of suppressing range ambiguous clutter.To extract the transmit-dimension range degrees of freedom,FDA incorporates multiple-input multiple-output(MIMO)techniques.Compared with the traditional MIMO radar,the FDA-MIMO radar can separate the range ambiguous clutter,which helps to improve the clutter suppression capability of the airborne radar.Therefore,this thesis focuses on the research on the airborne FDA-MIMO radar clutter suppression method,and mainly introduces the following aspects:1.The signal model of FDA-MIMO radar is established.Firstly,the basic signal model of FDA radar is established,and the range dimension,angle dimension and periodicity of its emission pattern are summarized.Next,the transceiver signal model and processing flow of MIMO radar are introduced,including matched filtering,beamforming,and the separation of transmitting dimensional degrees of freedom by matched filtering.Finally,the processing flow of the transmitter and receiver of FDA-MIMO radar is given,and the beam characteristics of the radar and the distribution characteristics of the target in the transmitreceive dimensions are studied.The non-adaptive beamforming can be used in fixed ranges and angles form peaks.2.Aiming at the three-dimensional clutter distribution and clutter degree of freedom evaluation problem under different array configurations of the airborne FDA-MIMO radar,the clutter spectrum characteristics of the side-looking configuration and the forwardlooking configuration are studied,and the clutter spectral characteristics are analyzed.The relationship between wave degrees of freedom and range ambiguity numbers.The clutter in both configurations has the problem of expanding the emission dimension,and a quadratic range-dependent compensation method is introduced,which can realize the focusing of the clutter.At the same time,by designing a reasonable frequency increment,the clutter in the different range ambiguous areas can be distinguished.Due to the array configuration,the clutter spectrum in the forward looking situation causes the three-dimensional characteristics of the clutter transmit and receive Doppler to change with range,and the clutter spectrum expands in three-dimensional space.Aiming at the range-dependence brought by the forward looking configuration,an adaptive three-dimensional angle Doppler compensation method is proposed.On the basis of separating range ambiguous clutter,the method compensates for the non-uniformity of the clutter in the range and improves the target detection performance.Finally,the projection of the three-dimensional clutter spectrum in the transmit-receive domain of the front-side-looking uniform linear array is studied,and the relationship between the clutter degrees of freedom and the range ambiguity number is analyzed.3.Aiming at the problem of range ambiguous clutter suppression for airborne FDA-MIMO radar,a range-angle Doppler three-dimensional adaptive processing method is studied.Compared with traditional space-time two-dimensional processing,FDA-MIMO radar can separate the range ambiguous clutter,and its three-dimensional adaptive processing increases the emission dimension,and has a good clutter suppression ability when the samples are sufficient.On this basis,the dimensionality reduction and rank reduction processing methods are studied,and the three-dimensional multi-channel joint processing method,the three-dimensional joint domain localized(JDL)processing method,the processing method based on sum-difference beam and the principal component method are analyzed in detail.Under ideal conditions,the JDL dimensionality reduction processing method reduces the IID sample requirements and calculation amount,and also has better clutter suppression performance.When further considering the existence of array element amplitude and phase errors and clutter fluctuations,a multi-channel joint processing method based on the time-domain sliding window is proposed.The method uses sliding window processing and Doppler filtering to select the outputs of several Doppler channels for joint adaptive dimensionality reduction processing to achieve clutter suppression.The effectiveness of the method is verified by simulation.