6.1 INTRODUCTION

The purpose of Chapter 6 is to address the capabilities and needs of airborne early warning (AEW) radar. Figure 6.1, derived from Toomay [1], helps to depict the environment of airborne radars, namely:

• radar-earth-target geometry, with its associated problems of atmospheric refraction, attenuation, and multipath effects

• relative aircraft-earth-target velocities, with the associated Doppler-processing challenges

• restrictions on frontal area and weight that limit antennas to relatively small sizes, which thereby contribute to poor angular resolution and increased Doppler spreading

• complex aircraft/antenna geometry, which contributes to larger antenna side-lobes and distortion of the main lobe

• jamming and other electromagnetic interference.

Figure 6.1: Airborne environment (after Toomay [1]).

AEW radars use two basic modes of operation: (1) the Doppler mode to detect moving aircraft over land and sea, and (2) the ordinary pulse or non-Doppler mode for detecting stationary or slow-moving targets such as boats or ships. The long-range Doppler detection mode, with its requirements made stringent by operating from a moving platform, distinguishes the AEW radar from others.

Principal problems associated with detection at long range of moving, low radar cross section (RCS) targets include:

• target echo level relative to receiver noise

• target echo level with respect to average background clutter caused by surface echo (land and water)

• the processing and subsequent elimination of false targets generated by strong stationary targets such as buildings, cliffs, water towers

• the processing and subsequent elimination of unwanted moving nuisance targets such as automobiles, birds, boats