2.1 Target models

All radar targets can be classified into point and complex targets ^[138]. A point target is a convenient model object commonly used in radar science and practice to solve certain types of problems. It is defined as a target located at distance R from a radar at the viewing point 0 , which scatters the incident radar radiation isotropically. For such a target, the equiphase surface is a sphere with the centre at 0 . Suppose a radar generates a wave described as

where f ₀ = ? _o/2 ? is the carrier frequency, while a and ? are the amplitude and phase modulation functions overlapping the carrier frequency.

A point target located at distance R creates an echo signal

where ? is a complex factor including the target reflectance and signal attenuation along the track.

The Doppler frequency shift is implicitly present in the variable R. If we assume that the radial velocity v ₁ is constant, we shall have

where R ₁ is the distance to the target at the initial moment of time t = 0.

Equations (2.1) and (2.2) describe a simple model target to be further used for the analysis of the aperture synthesis and imaging principles.

In practice, most radar targets refer to the class of complex targets. In spite of a great variety of particular targets, we can offer a common criterion for their classification. This criterion is based...