Overview

Radar echoes are a mixture of wanted echoes (for example, aircraft) and clutter echoes (often from land, sea, weather, or birds), which are generally of no interest. Signal processing tries to filter the echoes for the user and match them to his display. Modern digital processing often causes the echoes to be displayed as synthetic shapes that show only the information for which it has been preprogrammed. In contrast, radar operators who use older equipment are used to identifying echoes by size, shape, and movement. The evaluation of these criteria takes time and greatly reduces the number of echoes that an operator may follow, but it may be critical in unusual or unforeseen situations.

This chapter describes the filtering of echo signals according to Doppler frequency and also the judging of the correct threshold when clutter is present. The statistical consideration of signals and noise with Swerling model echoes is described in Chapter 12.

The echo signals from the receiver are the sum of the following, as shown in Figure 11.1:

• Echoes from objects illuminated by the main antenna lobe (leg A out, leg A back);

• Echoes from objects illuminated by the antenna sidelobes and received through the sidelobes (leg C out, leg C back);

• Echoes from objects illuminated by reflections from the antenna mainlobe and received through a sidelobe (leg C out, leg B, leg A back) when the mainlobe points towards the town clutter;

• Echoes from objects illuminated by the antenna mainlobe and received by reflection through...