Research On Target Localization And Imaging Using Frequency Diverse Array Radar

As is known,many advantages have been shown in Phased Arrays(PAs).However,some issues of target detection and parameter estimation exist in PAs since its beam-pattern is only angle-dependent.This angle-dependent beampattern indicates the range-dependent interference and clutters cannot be effectively suppressed.Meanwhile,range-angle localization and imaging of the targets cannot be obtained directly from the PA's beampattern.Generally,the range information is obtained by using broadband signals.While,frequency diverse Array(FDA)can generate a range-angle-dependent beampattern which can suppress the range-dependent interference and clutters,thus leading to many promising applications such as joint range-angle localization and imaging.In this thesis,the existing problems in target localization and imaging using FDA are considered,which are ambiguous target localization caused by the unsatisfactory range-angle decoupling method,and the array designs when linear FDA is extended to planar FDA.As a result,the efficient and reliable decoupling methods are proposed,then two-dimensional localization and three-dimensional imaging of the targets are achieved by combining effective signal processing method and reasonable array design.The main research contents are as follows:(1)The double-sideband frequency diversity array(DS-FDA)radar system is proposed.Two localization method for DS-FDA are presented,i.e.the single-target localization method based on receive beamforming,and the multi-target localization method based on subspace decomposition.Since the beampattern generated by positive frequency increment and by negative frequency increment are opposite and symmetrical,the range-angle decoupling is achieved by using both the upper and lower sideband.Compared with the multi-carrier decoupling method,DS-FDA has lower complexity in transmit signal and waveform optimization method.In addition,only one single transmit pulse is required in DS-FDA and the decoupled regular beampattern shape has a higher resolution when compared with the double-pulse FDA.(2)The random permutated FDA is proposed to solve the problems in random FDA as in random FDA,the decoupling method is unreliable and the idle bandwidth is overlooked.In the proposed random permutated FDA,the criterion of identifying the frequency increment coefficient vectors causing ambiguous localization is presented.By deriving the analytical relationship between the frequency increment coefficient vector and the ambiguous target localization,the reason of ambiguous localization is revealed,which is the linear correlation among different combinations of random frequency increment coefficient and the array location coefficients.According to the algebraic relation between the frequency increment coefficients,the criterion of identifying the frequency increment coefficient vectors causing ambiguous localization is designed.Different with the existing design methods of frequency increment coefficient vector,the proposed criterion can obtain reliable identifying results for each deterministic frequency increment coefficient vector.(3)In multi-target localization using random permutated FDA,the ambiguous localization may occur due to the target relative locations.Here,the criterion of identifying the frequency increment coefficient vectors causing ambiguous localization for two targets and multitargets are proposed,respectively.The reason of the ambiguous localization for two targets is revealed.When the two targets meet the minimum periodicity condition,a new linear relationship between the frequency increment coefficient and the matrix position coefficient is introduced.The rank-deficiency of the relation matrix produced by the target locations is demonstrated as the principle of the ambiguous localization for multitargets.Accordingly,the criterion based on the algebraic relation of frequency increment coefficient and the criterion based on the rank of relation matrix are designed to further constrain the random frequency increment to realize the unambiguous multitargets localization.(4)The above efficient and reliable decoupling method makes FDA easy to extend to two-dimensional planar arrays.The decoupled planar FDA can obtain a 3-D dot-shaped beampattern that is more regular than the traditional planar FDA.However,due to the large number of array elements,the two-dimensional antenna may have large size and more filters,which makes it difficult to be implemented in the practical scenarios.To solve this problem,a frequency diversity array synthetic aperture three-dimensional imaging(3D-FDA-SAR)system is proposed.By exploiting a frequency diversity array instead of the real array in 3D-SAR,the complexity of the radio-frequency head of 3D-SAR and the complexity of the planar FDA can be reduced.In the 3D-FDA-SAR,a trade-off between space resources and time resources can be achieved,thereby meets the requirements of the imaging system in terms of cost performance,real-time performance,and resolution at the same time.