| As an extension of phased array(PA)radar,frequency diversity array(FDA)radar can be considered as a generalized phased array radar.On the basis of PA radar,the most significant difference of FDA radar is that the FDA radar introduced a tiny frequency offset across the transmitting array elements,which will help to generate a range-angle dependent transmit beampattern.Therefore,compared with the conventional phased array,the beampattern of the FDA radar has two-dimensional degrees-of-freedom of the angle dimension and the range dimension,respectively.Therefore,FDA radar has great application potential in the target multidimensional parameter estimation,mainlobe interference suppression,secure communication,integrated design,and other applications.Focusing on several hot issues about FDA radar in current research,this dissertation investigated the coherent receiver design,multi-dimensional parameter joint estimation,deceptive jammer suppression and beamforming of FDA radar.The main research work of this dissertation is summarized as follows:1.For the problem of FDA radar receiver in the form of transmitting spectrum overlapping linear frequency modulated(LFM)signal,a receiver structure based on fractional domain signal separation method is proposed in this paper.The theoretical procedure of signal separation in the optimal fractional domain is deduced in detail.The signal separation method consists of two steps: 1)Calculated the optimal rotation angle according to the frequency modulation slope of the transmitted LFM signal and performed the fractional Fourier transform(Fr FT)of the optimal rotation angle for received signal;2)Take each peak point value of Fr FT result and perform inverse Fr FT of the optimal rotation angle to obtain the separated signal.The separated signals obtained from the proposed receiver architecture lay a theoretical foundation for signal processing such as parameter estimation,beamforming,and interference suppression.Compared with the multi-channel mixing receiver structure designed based on sufficient statistics,the proposed receiver structure simplifies the structure,saves resources,and ensures receiver performance.2.For the joint parameter estimation problem of linear FDA radar with non-uniform frequency offset,a two-step parameter estimation method and a decoupling parameter estimation algorithm are proposed,respectively.For the two-step estimation method,the first step is to estimate the angle,and then the estimated angle result is substituted into the range estimation.For the decoupling parameter estimation algorithm,the range-independent and rangeindependent data vectors are constructed first by matrix transformation,and then the parameters of the independent data vectors are estimated respectively.Compared with the two-step estimation method,the decoupling parameter estimation method has the advantage of independent parameter estimation accuracy.In addition,according to the special transmission signal form of FDA radar,an unambiguous velocity estimation method based on phase difference between array elements is proposed.This velocity estimation method solves the Doppler dilemma in conventional radar and the maximum unambiguous velocity is no longer constrained by the pulse repetition period and wavelength.3.For the problem of beampattern decoupling and three-dimensional parameter estimation of FDA radar,a three-dimensional parameter estimation method of uniform circular FDA(UCFDA)radar is proposed.Firstly,according to the transmitting array structure and signal model of the UC-FDA radar,the decoupling capability of the transmitting beampattern is comprehensively analyzed.And then,according to the receiving signal model of the UC-FDA radar,the target three-dimensional parameter(azimuth,elevation,and range)estimation method is proposed.In the three-dimensional parameter estimation method,the received data of the UC-FDA radar is first performed matrix transformation,and then the transformed matrix is used to estimate the azimuth and elevation parameters,and finally the estimated azimuth and elevation parameters are substituted for range parameters estimation.The results show that the UC-FDA radar has natural beampattern decoupling capability due to its special array structure,not only that,it also has the capability of range-azimuth-elevation three-dimensional information acquiring and localization.4.For the problem of mainlobe deceptive interference suppression,a range deceptive interference discrimination method for FDA radar based on staggered frequency offset is proposed,and the deceptive interference suppression is performed by an improved range-angle two-dimensional adaptive beamforming method.In this thesis,the range deceptive interference is divided into three types.First,the true target and deceptive interference are discriminated according to the different transmit-receive spatial frequency distribution.And then the range-angle two-dimensional adaptive beamforming is performed for deceptive interference suppression.The effect of deceptive interference on the main lobe distortion in angular beamforming and the interference jitter in range beamforming is fully considered in two-dimensional adaptive beamforming.Therefore,a two-dimension adaptive beamforming method with angledimension mainlobe shape-preserving and range-dimension null broadening is utilized.The proposed deceptive interference discrimination method has the advantage of engineering feasibility,and the improved two-dimensional adaptive beamforming method has better robustness for deceptive interference suppression.5.For the problem of target adjacent interference suppression,a robust beamforming method based on aperture expansion is proposed to improve beam resolution for target adjacent interference suppression.Firstly,the transmitting and receiving steering vectors in the observation data model of the FDA radar are transformed into the range and angle steering vectors after the aperture expansion,respectively.And then,according to the actual steering vectors and expansion steering vectors,the interference-noise covariance matrix and the desired target signal covariance matrix are reconstructed,and the desired target steering vector is also upgraded,so that it is projected onto the signal space after aperture expansion.Finally,the robust beamformer weight vector of the proposed aperture expansion method is obtained.The proposed method improves the beam resolution of FDA beamforming which has superior robustness to suppress target adjacent interference. |
PDF Full Text Request