Study Of Simplified STAP And Its Application To Airborne Radar

Clutter suppression is critical to airborne early warning surveillance sensors. In addition to the conventional techniques such as low sidelobe antennas and displaced phased center antenna (DPCA), there has been great interest in space-time adaptive processing (STAP) because it can suppress clutter effectively and improve the detection performance of airborne phased array radar evidently. The research on STAP began in!973 and has been performed for more than 20 years. In the beginning, the focus is on the theory of optimum full rank STAP. But the computation load and the implementation complexity of full rank STAP are too great to be accepted and it is really very difficult to obtain enough samples to estimate the covariance matrix. The focus of successive research is concentrated on the reduced-rank algorithms and many reduced-rank methods have been proposed. The reduced-rank methods usually can be divided into two groups: the fixed ones and the adaptive ones. To implement STAP in engineering the fixed (non-adaptive) methods are more interesting because they have the advantages of simpler structure and lower computation load. The fewer spatial degrees-of-freedom(DOF) are always hoped. With the progress in STAP being made continually, people find STAP can be used in many other radars besides airborne early warning surveillance radars if only the clutter is space-time-coupling. The ground moving target detection (GMTI/GMTD) is an important function of the battlefield awareness radar and fighter's fire-control radar. In the GMTI/GMTD the ground clutter will do strong harm to the detection and STAP can be used to suppress the clutter. The main purpose of this dissertation is to study a simplified STAP and its application in GMTD.In 1996, H.Wang et. al. proposed a new reduced-rank STAP which has only two spatial degrees-of-freedom(DOF). They call it ?A -STAP because the two channels are the sum and difference beams of the antenna. Their interest in ?A -STAP stemmed from the fact that antenna engineers have excelled in the design of high performance sum and difference beam whether for phased array or for reflector antenna. So their method can be used not only for phased array radar but also for reflector antenna radar. Their research shows the ?A -STAP can provide good clutter-suppression performance and has many advantages. But it also has many limitations and in somecases its performance is not satisfying.In the beginning of Chapter 2 the principles of the fixed reduced-rank methods and the constant false alarm rate (CFAR) detection are described. Then several Doppler-domain reduced-rank methods are discussed including a Doppler-domain ?A -STAP approach which is called ?A -EFA (Extended Factored Approach). Analysis and simulations are given showing that the 2 A -EFA has satisfying clutter suppressing performance and the better space-time respondence in ideal system condition. But in actual condition the performance of 2 A -EFA will degrade seriously. So in Chapter 3 some non-ideal conditions are considered. They are the property of sum and difference beams, the errors of the elements and channels and different pulse repeating frequency (PRF). These parameters have evident influence on the clutter suppression. The influence of these parameters and the limitations of ?A -EFA are studied. Then an improved ?A -EFA are proposed which can break most limitations of the original ?A-EFA.In Chapter 4, non-adaptive methods and the simplified STAP for GMTD are discussed using the side-looking array. The DPCA and interferometer are usual non-adaptive methods to suppress clutter for GMTD. Their weights vary with the velocity of the platform and the requirements of the precision and the data-rate of the INS or GPS are very high At the beginning the distribution of the space-time spectrum of the clutter is studied. The space-time spectrum is seriously ambiguous and the clutter of mainbeam is the most important obstruct hi detecting the moving targets. Then the principle of the interferometer approach is desc...