Research On Non-Adaptive Clutter Suppression Algorithms For Airborne Radar

In recent years, the phased-array is widely applied in the airborne radar. In order tosuppress the spatially-temporally coupled clutter which is induced by the movement ofthe airplane, the well-known space-time adaptive processing (STAP) algorithms arevigorously researched. As the number of the array antennas and the dimension of thesignals become larger and larger, the problems of the computational complexity and thetraining samples required become more and more serious. Thus, the suboptimaldimension-reduced STAP algorithms have been rapidly developed, too. However,compared with the above adaptive algorithms, the research of non-adaptive algorithmsis relatively insufficient. Since the non-adaptive algorithms have low computationalcomplexity and less demand for the training samples, they are more suitable for thereal-time processing. Hence, this paper will mainly focus on the non-adaptive cluttersuppression approaches in both the airborne phased-array radar and the airbornemultiple-input-multiple-output (MIMO) radar. The main contributions of the thesis aresummarized as follows:1. The spatial-temporal model of the clutter data for the airborne MIMO radar isestablished. Taking full advantage of the prior information such as the radar parametersand the platform velocity, we proposed a multiple-input-multiple-outputtwo-dimensional pulse-to-pulse canceller (MIMO TDPC). A least-square cost functionassociated with the coefficient matrix of the MIMO TDPC is organized, and thecoefficient matrix is obtained by solving the optimization problem. Since the MIMOTDPC coefficient matrix can be calculated by using the prior information, our method isa non-adaptive method which owns low computational complexity andnon-convergence process. As an efficient and convenient ground clutter pre-filteringtool before the conventional moving target indication (MTI) method and thewell-known suboptimal dimension-reduced STAP algorithms, MIMO TDPC caneffectively enhance the target detection performance. Furthermore, the drift angle isadopted in the design of our method. Thus, MIMO TDPC can be utilized in bothsidelooking radar and non-sidelooking radar.2. In order to suppress the short-range heterogeneous clutter for the non-sidelookingairborne radar (non-SLAR), we propose a short-range clutter suppression approach(SCSA). Space-time adaptive processing (STAP) methods which have been developed for suppressing the spatially-temporally coupled ground clutter in the airborne radarhave achieved good performance when applied to the sidelooking airborne radar (SLAR)where the clutter is relatively stationary. However, due to the range dependence (or thegeometry-induced heterogeneous clutter) the performance is degraded in the non-SLARespecially for the short-range clutter suppression where the range dependence is moresevere. Thus, the SCSA is established based on the geometry knowledge of the clutter,the radar parameters and the platform velocity for suppressing the short-range clutter inthe non-SLAR. The SCSA is composed of two parts the spatial-temporal pre-filteringand the spatial-temporal matching. Since the target detection performance of theclassical adaptive algorithms will be degraded by the range-dependent secondarysamples, the SCSA which is a non-adaptive algorithm can gain a relatively goodperformance. Moreover, compared with the adaptive algorithms the computationalburden of which is high due to the covariance matrix inverse operation, the SCSA whichcan be pre-calculated and made into a look-up table is more suitable for the real-timeprocessing.3. The variation of the airborne radar platform velocity will cause the clutterfluctuation, and thus lead to the clutter power spectrum widening along the cluttertrajectories in the angle-Doppler domain. On the basis of the clutter model, a noveltwo-dimensional multi-pulse canceller (TDMC) which employs more pulses of theclutter echo is established. Compared with the existing two-dimensional pulse-to-pulsecanceller (TDPC) which adopts only two pulses of the clutter echo, the TDMC utilizesmore degrees of freedom (DOFs) to organize a spatial-temporal two-dimensionalband-rejection filter to suppress the ground clutter more efficiently. Experiments of bothsimulated data and measured data show that the proposed TDMC can gain a bettertarget detection performance than the TDPC, especially for the slow-moving targetdetection.