Research On Key Technologies Of MIMO-SAR

MIMO-SAR has broad prospects in the realization of high-resolution imaging,wide mapping band imaging,etc.,and has become a hotspot in the current radar field.In the high-resolution wide-range imaging,there is a problem: the wide mapping band of the system in the distance direction causes the system to use a low pulse repetition frequency(PRF)to avoid distance blurring,but the low PRF brings the undersampling of the azimuth,which results in ambiguity in the resulting image.MIMO-SAR,as a multitransmission and multi-reception SAR imaging system,can improve the sampling rate of the azimuth without changing the system's PRF.It is a powerful method to solve the problem of the high-resolution wide-range imaging.In order to achieve high-resolution and low-sidelobe imaging of MIMO-SAR,the MIMO array must be reasonably designed,and transmit waveforms have good orthogonal performance and transmit / receive channels meet amplitude-phase consistency.This paper mainly studies on the three key technologies of MIMO-SAR: the correction of channel amplitude and phase error,the design of orthogonal waveform and the design of array arrangement.The main research contents and innovations of this article are as follows:1.The basis of traditional SAR and MIMO-SAR,as well as the causes of azimuth blur and MIMO-SAR-based azimuth blur suppression methods are briefly described.First,the SAR echo signal model and the traditional SAR imaging algorithm are introduced.Among them,the backward projection imaging algorithm is mainly introduced.Then,the signal model,working principle and phase center equivalent principle of MIMO-SAR are introduced.Finally,the principle of azimuth ambiguity suppression of MIMO-SAR system is given.2.The channel amplitude and phase error correction of MIMO-SAR system is studied.Firstly,it analyzes the existence of amplitude and phase errors in the channel,which will lead to the decrease of the main lobe,the increase of the side lobe,and even false targets.Then,a channel amplitude and phase error estimation method based on single-strength target imaging is proposed,that is,in real-aperture imaging on a singlestrength target,the ratio of the maximum value of the one-dimensional distance of the echo pulse pressure results of each channel is used as the channel's amplitude error,and then use the maximum image sharpness as the objective function to estimate the phase error through the optimization method.The simulation results show that the proposed channel amplitude and phase error estimation method has high accuracy.3.The design of orthogonal waveforms for MIMO-SAR is studied.Firstly,the crosscorrelation function and point target simulation results are used to verify that the orthogonality of the short-term shift orthogonal signals are better than the positive and negative signals within the time delay.To solve the problem of the orthogonality of the short-term shift orthogonal signals get worse in the wide range imaging,we proposes a method based on polarization.By comparing with the imaging results that do not use the polarization method,it is verified that the proposed algorithm can solve the problem that the imaging of the short-term shift orthogonal signals in the large scene deteriorates without the false target in the imaging result.Finally,a kind of four-transmit orthogonal signals is proposed,and its orthogonality is verified by simulation.4.The construction method of MIMO-SAR array based on coprime array is studied.The principle and the constitution of coprime array are introduced first.Next,the coprime array is introduced into the SIMO-SAR system.Based on the principle of phase center equivalence,the actual array element position relationship of the SIMO-SAR and the coprime array and the relationship between the moving speed of the radar platform and the array length and pulse repetition frequency are analyzed.The construction of SIMOSAR coprime array is presented.On this basis,the simulation of the SIMO-SAR coprime array and uniform array verifies the feasibility of using the coprime array for SIMO-SAR imaging,and proves that with the same system simulation conditions and the number of array elements the coprime array can further improve the azimuth sampling rate and suppress the azimuth blur compared with the traditional SIMO-SAR uniform array.Finally,the construction method of MIMO-SAR's one-dimensional and two-dimensional coprime array under the conditions of the same or different PRFs of transmitted signals is proposed,and simulation proves that MIMO-SAR coprime array can improve the azimuth sampling rate to suppress azimuth blur.