| With the rapid development of modern electronic technology,radar is now facing a more severe environment,and new interference techniques are threatening the survival and the perfonnance of the radar.The mainlobe interference and the target have strong spatial cor-relation since they both are presented in the mainlobe direction.The Adaptive Digital Beam-forming is an efficient method for sidelobe interference suppression.But for the mainlobe interference,adaptive beamforming methods depress the target signal,and also results in beam distortion.In the meanwhile,for the DRFM repeated interference,the interference can intercept the radar signals and generate replicas that simulate false targets to confuse radar,hindering its ability to identify the true targets from the false ones in time domain or frequency domain.So the study on the new radar systems and the related interference suppression research are the imperious demands.As two kinds of the new radar systems,Frequency diverse array and polarimetric radar have unique advantage on interference rejec-tion.The Frequency diverse array adopts a frequency increment across the array elements,which increase the processing DOF in range.The polarimetric radar can discriminate and suppress the mainlobe interference from the polarization domain.However,the target signal is depressed as well when the polarization state of the target and the interference are the same.This dissertation focuses on the interference suppression problem with polarimetric frequency diverse MIMO radar,and the main content of this dissertation can be summarized as follows.1.The signal model and the beamforming problem for the frequency diverse array is stud-ied.Firstly the signal model of the frequency diverse array is introduced.The transmit beampattern is range-angle dependent by using a small frequency increment across the ar-ray element.Moreover,peak ridges are formed in the range-angle diagram.To obtain a single-peak transmit beampattern,the array configuration is put forward by analyzing the expression of the beamforming.Also,some specific examples are discussed.In addition,the array configuration for range-angle decoupling is introduced based on the parameter esti-mation theory and the deduction of the Cramer-Rao Bound.Lastly,the receive beampattern and overall beampattern are introduced.The numerical results verify the proposed theory.2.The deception interference suppression method with frequency diverse MIMO radar is studied.The transmit steering vector of the frequency diverse MIMO radar is range-angle coupled,providing extra DOF in range processing domain,which is beneficial for sup-pressing the range deception jamming.For the range deception jamming,the real range of the jammer is not matched to the range of the false targets.Based on this property,a range-matching based discrimination method is proposed.In addition,ESPRIT algorithm is used for estimating the angle and the range parameters.When suppressing the jamming by adaptive beamforming methods,the suppression performance is related to the correla-tion between the steering vectors of the true target and the false target.To obtain a better interference suppression performance,an optimization method for the frequency increment is proposed to minimize the correlation between the true target and the false targets.The numerical results verify that the frequency diverse MIMO radar can reject range deception interference efficiently,and with the optimal frequency increment,a significant higher out-put SINR can be achieved,especially for the multiple interference scenario.3.The mainlobe interference suppression method with the polarimetric MIMO radar is studied.The scattering matrix of the target is related to the attitude,the angle and etc.The polarization information of the target and the jamming are usually different,offering the ability to mitigate the interference from the polarization domain.Two different polarimetric MIMO radars are proposed:1)the polarization diversity is adopted in the transmit array,while the receive array is composed of the 2-D vector sensors to measure the horizontal and vertical components of the receive signal.Since the polarization state of the jamming is invariant,while the one of the target sensed by the receive element are different because of the polarization diversity in the transmit array.Based on the property,the discrimina-tion method for the false targets and the true target is proposed.Moreover,the polarization information in the signal model can be regarded as a amplitude-phase error matrix,which can be estimated by using self-calibration method.The adaptive beamforming method is used to suppress the jamming.Based on the anti-jamming performance analysis,a trans-mit polarization optimization method is proposed to obtain a better interference suppression performance.2)Contrast to the kind of the polarimetric MIMO radar mentioned before,in the second kind of polarimetric MIMO radar,the polarization diversity are both used in the transmit array and the receive array.Under this condition,the oblique projection operator is used to suppress the interference,and the anti-jamming performance is analyzed.The trans-mit and receive polarization optimization methods are proposed.The numerical examples verify that with the two kinds of polarimetric MIMO radar,the mainlobe interference can be efficiently suppressed.Moreover,a better performance can be achieved with the optimal transmit or receive polarizations.4.Statistical method with Dual-Polarized MIMO Array for target Discrimination is studied.A radar scheme called dual-polarized MIMO array is proposed,and study the target dis-crimination method under the active-decoys scenario with the proposed radar system.The configuration and the algorithm are easy to realize,which can be applied in practice.The polarization diversity is employed in transmit antennas and receive antennas.The target dis-crimination problem can be transformed into a binary hypothesis problem and design the Neyman-Pearson discriminator by statistical analysis.Otherwise,the discrimination per-formance for the true target and the false target are analyzed.The polarization searching method across the transmitter and receiver is studied.The numerical simulations demon-strate that optimal design of the transmitter and receiver polarizations provides improved discrimination performance over the radar with only horizontally and vertically polarized transmit antennas.5.The interference suppression performance with the polarimetric frequency diverse MIMO radar is studied.Since the large cost for the transmit polarization diversity,a different kind of polarimetric frequency diverse MIMO radar is proposed combining the advantage of the polarimetric MIMO radar and the frequency diverse MIMO radar.In this radar,the transmit elements are single-polarized,and the receive array is composed of the 2-D vector sensors.The radar can use the range,spatial and polarization information at the same time.The output SINR is related to the spatial correlation and the polarization correlation between the interference and the target,and the spatial correlation is a function of range and angle.The better anti-jamming performance can be achieved by decreasing the spatial correlation and the polarization correlation. |
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