Research On Cognitive Frequency Diversity Imagin Technology

Frequency diversity Array(FDA)evolved by the phased Array radar is a special form of Array radar.Its transmitted beam pattern is dependent on angle and distance,and can scan in space without relying on phase shifters,which makes frequency diversity Array radar has great application prospects in target location detection and imaging.This paper mainly focuses on the problems of fuzzy target position,high sidelobe and insufficient imaging adaptive ability during frequency diversity array radar imaging.With the help of cognitive theory,research effective algorithms to complete FDA multi-target high-quality two-dimensional imaging.The main research contents proposed are as follows:1.In order to solve the problems of poor imaging effect and weak adaptive ability of FDA radar for multi-target imaging,a frequency diversity array radar target imaging method based on clustering coherent superposition is proposed.On the basis of analyzing and simulating the BP algorithm imaging process,it is found that the target point has the characteristics of energy concentration.The K-means clustering algorithm can make full use of these characteristics of the target points,to perform feature recognition and classification of the target points,and only perform delay compensation on the grid points of a specific cluster after classification,thus obtain high-quality two-dimensional image.Simulation experiments show that this method can effectively eliminate false images of the target,and at the same time eliminate the influence of the side lobes,and obtain a clear two-dimensional image.However,this method also has some shortcomings.In the noisy environment or when the scattering intensity of different target points is quite different,the two-dimensional imaging of multi-target is blurred.2.Aiming at the problems of the first method,a CLEAN based FDA image reconstruction algorithm is proposed.Based on the analysis of the double-sideband frequency diversity array radar model,it is found that the frequency increments of the upper and lower sidebands are(35)f and-(35)f respectively,the slopes of the transmitted beam pattern formed are opposite to each other.So make full use of this feature,only need to transmit a pulse signal once,and use the BP algorithm to perform coarse imaging of multiple targets.Then the CLEAN algorithm is introduced into the coarse image processing.By searching and iterating the image,the position of the target is proposed from the image according to the order of the intensity,the scattering coefficient and the corresponding PSF function are calculated,finally realized through image reconstruction,a high-quality two-dimensional FDA image is obtained.Simulation experiments show that the proposed algorithm can also reconstruct high-quality two-dimensional image of the target,in the case of low signal-to-noise ratio and large difference of scattering intensity.3.Aiming at the limitation of the number of FDA array elements and the number of targets in the above method,an adaptive adjustment imaging algorithm of FDA array elements based on cognition of target number is proposed.Through feature recognition of the target,the transmitter adaptively adjusts the number of transmitting array elements according to the recognition results and prior knowledge,so that the number of transmitting array elements changes with the number of targets.Simulation experiments show that this method can achieve the number of array elements to change with the number of targets under the premise of obtaining the reconstructed high-quality image,which improves the utilization rate of radar array elements.