4.1 Introduction

In Chapter 3, the high-range resolution techniques discussed were appropriate to down range of the radar, along its radial vector. The range resolution obtained depended upon the bandwidth of the waveform transmitted. In this chapter, techniques for providing high cross-range resolution are presented, which correspond to the direction perpendicular to the radar's radial vector. As was briefly presented in Section 2.2.4, cross-range resolution is basically dependent upon the aperture of the antenna employed or the aperture that is synthesised by virtue of the motion of either the radar or the target. In some circumstances, when both the radar and the target are in motion, the synthesised aperture is dependent upon both of these motions.

In Section 4.2, Doppler beam sharpening is discussed. This is a high cross- range resolution technique, which is dependent upon the radar being located on a moving platform and utilising a coherent pulse Doppler waveform for providing increased cross-range resolution using the Doppler effect. It can contribute to target recognition by isolating individual targets in azimuth, but the actual cross-range resolution obtained would not normally be sufficiently high to resolve individual target scatterers.

In Section 4.3, SAR is presented, which provides high cross-range resolution by synthesising a large antenna aperture, due to the motion of the radar. This effectively decreases the beamwidth of the radar and a very narrow beam is synthesised, which provides high cross-rangere solution and varies with target range for a fixed integration time. Various types of SARs are presented, which...