Study On Several Key Issues Of STAP Technology For Airborne Radar Clutter Suppression

The airborne radar system platform is installed on the aircraft,which can effectively overcome the influence of unfavorable factors such as ground blockage and earth curvature.It has the advantages of wide field of vision,flexible deployment,and strong maneuverability,so it has been widely used.However,due to the clutter of strong ground objects working under the airborne radar,and the clutter in different azimuths have different Doppler frequencies,that is,the clutter of the airborne radar has the characteristics of space-time coupling,so it is difficult to suppress clutters effectively only through the time or space domain filters,and the target signals completely submerged under a strong clutter background are too difficult to detect.Therefore,clutter suppression is the primary problem which can be solved by airborne radar to achieve MTD,and STAP(Space-Time Adaptive Processing)technology provides an effective solution method for airborne radar to achieve clutter suppression.However,traditional STAP converges to a steady-state solution that requires independent and identically distributed samples equal to 2 times the dimension of the space-time adaptive filter.Even for dimensionality reduction or rank-reduction STAP,a considerable amount of IID training samples are required to satisfy the condition that the loss of the output signal-to-interference ratio is less than 3d B compared to the optimum filter.In practical applications,due to the influence of various environmental factors,which causes the non-uniformity and non-stationarity of the airborne radar’s working environment under the look-down work pattern,the number of IID training samples with twice the dimension of the space-time filter is often difficult to guarantee,thus it seriously affects the clutter suppression performance of STAP.After decades of development,on the base of the traditional STAP technology,various of methods such as KA-STAP under non-uniform,STAP based on sparse recovery are invented,and the performance of these methods in clutter suppression,target signal detection have made great improvements,but the small sample size,non-uniform and non-stationary practical application environment are still the main reason for the serious degradation of STAP clutter suppression performance.The pre-whitened STAP algorithm in the existing KA-STAP algorithms,although can obtain fast convergence rate in ideal conditions,but in practical applications,the existence of various types of array errors seriously affect the performance of the pre-whitened STAP algorithm.However,although the existing array error correction algorithms based on KA-STAP have achieved good correction performance,the steps which be used to correct the array elements amplitude and phase errors,array element position errors and array element mutual coupling effects separately are more complicated,and all kinds of errors are azimuth-dependent,so even if all kinds of errors are combined to be corrected,it is necessary to use the correction sources of each incident direction to sequentially correct the combined errors of each incident direction,which is time-consuming.In the field of radar signal processing,the LFM signal(or Chirp signal)is a mature low-interception probability signal with high radiant energy and high range resolution ability.Due to its ultra-wideband characteristics,LFM signals have important applications for all kinds of radar systems.But at present the existing wideband LFM-STAP models have the two problems as follows,complicated expression and inconsistent with the traditional STAP expression.Therefore,they not only cause the algorithm under the wideband LFM-STAP model to be too complicated,but also cannot use some of the traditional STAP algorithms for data processing.In response to these two problems,this dissertation carried out corresponding technical research,the specific research content is as follows:In view of the corresponding problems of the array error correction algorithm based on KA-STAP for narrow-band airborne radar,this dissertation does not estimate the impacts of these three types of errors of array element amplitude and phase error,position error and mutual coupling effect on KA-STAP separately,but regards these three types of errors as an integral whole,that is,the integrated error of the array for overall correction.And it is proposed that when the airborne radar is stationary on the ground or hovering in the air to take all the antenna beam directions and the corresponding angle reflector correction source incident directions throughout all directions of the airborne radar array antenna beam direction set ?,in order to obtain the comprehensive error estimation database.This database can realize the correction of the prior CCM(clutter covariance matrix)and the target space-time steering vector.In response to the problems that the existing wideband LFM-STAP model has a more complicated form,which is not conducive to CCM estimation and some follow-up work,this dissertation modifies the wideband LFM-STAP model,and this modified model is not only an improvement of the traditional STAP model to make it suitable for wideband conditions,but also uses the various processing algorithms and processes of traditional STAP make it easy to follow some of the traditional STAP algorithms for data processing.In using of performing clutter suppression under the wideband LFM-STAP model,have the small sample size or non-uniform and non-stationary problems,this dissertation introduces the KA-STAP algorithm to this model to reduce the requiring amount of IID training samples for the system while performing clutter suppression.