13.1 Introduction

The function of most radar systems is to supply data about the presence and position of targets of interest [1]. A typical radar system emits an electromagnetic pulse and analyses the reflections of the transmitted energy. Ideally, the radar system will detect returns from range cells that contain targets and will reject returns from range cells that contain only background energy. A range cell represents a small block of physical space that is a certain distance (range) from the receiver. The radar checks for a target in each range cell of interest, typically referred to as a test cell. Range cells other than the test cell are called reference cells. The target signal competes with background energy that is potentially composed of a combination of thermal noise, clutter and jamming.

Thermal noise is caused by the thermal agitation of electrons and is present in all real receivers. In this chapter, we consider radar arrays in which each antenna element has its own receiver. Therefore, the thermal noise at each antenna element is considered to be independent of the thermal noise at the other elements.

Radar clutter is generically defined as the echoes from scatterers that are not deemed to be of tactical significance [115]. For airborne surveillance radar, the ground is the major source of clutter. Ground clutter is distributed in both angle and range. It is also spread in Doppler frequency due to the motion of the array...