Research On Imaging Algorithms Of Monostatic Metamaterial Apertures-Based Radar

With the rapid development of information technology and the new military revolution,the use of various intelligent and unmanned combat weapons is the developing trend of future battlefield.The capability to have a fast,accurate and fine perception for the complicated external environments is vital for unmanned combat weapons,and the normal work of un-manned combat weapons is ensured by various sensors.It is therefore of great significance to investigate a sensor with small system form-factor and able to achieve accurate perception of the external environment in all kinds of complex working environment.Combined with the three-dimensional high-resolution imaging capability and the relatively flexible system component of the metamaterial aperture antenna(MAA),it will have evident advantages in future application for imaging sensor of an unmanned platform.This dissertation mainly focuses on the topic of the novel inetamaterial aperture imaging radar.For the goal of achiev-ing environment sensing,the unavoidable problems concerned with the limitation of system measurement modes and the tremendous computation cost and low imaging efficiency are researched in detail.The main research work can be concluded as:(1)Study on the degree of freedom evaluation of the MAA random radiation field.An evaluation index which ables to indicate the imaging performance of the MMA measure-ment modes is needed to guide the MMA optimization.In this paper,an evaluation index is proposed to bridge the front-end design of the system parameters of the MAA and the cor-responding imaging performance of MAA radiation fields.The evaluation index uses both the first-order and the second-order statistic of the correlation matrix of the measurement matrix.Besides,a phase transit diagram is figured to illustrate the direct relation between the measurement matrix correlation character and imaging performance of the measurement matrix.(2)Study on enhancing the imaging performance of MAA.Aiming at the problem that the number of measurement modes of MAA imaging system is limited when performing large-scale scene space imaging,an aperture rotation synthesis is proposed to increase the number of system measurement modes and improve the scene imaging quality.Firstly the Fourier transform correspondence between the spatial spectral domain sampling of the imaging sys-tem and the target scattering coefficient is mathematically derived with the Diffraction To-mography algorithm,and the internal physical mechanism of the effectiveness of the rotat-ing synthetic imaging algorithm is theoretically illustrated.Then the enhancement of the measurement modes achieved by aperture rotation interval and rotation times are discussed respectively,and the imaging simulation is conducted to validate the effective improvement of the image quality.(3)Study on enhancing the imaging efficiency of the MAA imaging system.When MAA performs high-resolution three-dimensional scene imaging,the dimensions of the measure-ment equation built under the forward imaging model are of extremely high dimensionality,which generally resulting in heavy computation costs and large memory storage,and the imaging efficiency is relatively low.Aiming at this problem,a fast parallel imaging post-processing algorithm based on range coupling algorithm is proposed in this paper.By using the inherent local stationary characteristics of the MAA radiation field patterns,a sliding-window processing algorithm is designed to ensure the stability of the random pattern in full operation band consideration.Then,an updated measurement equation is constructed to re-construct different scene space images in a parallel fashion,yielding dramatically increased forward imaging efficiency.(4)Study on the synthetic aperture radar imaging with MAA.Aiming at a hybrid three-dimensional imaging system which combines real aperture imaging and synthetic aperture imaging,two fast post-processing algorithms are proposed in this paper.The key post-processing lies in the decoupling between the antenna movement dimension and the antenna lengthwise direction.In order to realize the decoupling,firstly,a near range beamforming process is performed on the spatial sampled echo data by using the principle of wide beam synthesis in the Back Projection algorithm,and the azimuth response functions of different azimuth angles in scene space are obtained.For each azimuth angle sector,two-dimensional(slant-range and elevation angle)reconstruction was performed with computational imag-ing algorithms.Then the Stolt interpolation algorithm in Omega-K algorithm is used to achieve the decoupling between the azimuth wavenumber and the range wavenumber in the wavenumber domain,and the Fourier transform is performed to achieve azimuth focusing.The elevation and range dimension can further be reconstructed with the knowledge of the MAA field pattern.The effectiveness of the proposed post-processing algorithms in this dissertation are demon-strated with a large number of both the simulated and measured radiation fields data.The achieved research results have certain practical effects on the imaging processing of the practical MAA imaging radar.