Page 111 - Fundamentals of Radar Signal Processing

shifted relative to the carrier by the amount –4πR/λ radians. As will be seen,

this range-dependent phase shift provides the basis for most fundamental
coherent radar signal processing operations such as Doppler processing,
imaging, and adaptive beamforming. The phase shift is a very sensitive, but also
very ambiguous, indicator of range changes since every λ/2 change in range
produces a 2π change in phase.

The RCS σ is proportional to . Define

(2.50)

and

(2.51)

RCS variations like those of Fig. 2.6 become very complicated for
complex targets having many scatterers of varying individual RCS. Figure 2.8
shows a “target” consisting of 50 point scatterers randomly distributed within a
rectangle 5 m wide and 10 m long. The RCS of each individual point scatterer is
a constant, σ = 1.0. Figure 2.9 shows the relative RCS, computed at 0.2°
i
increments using Eq. (2.51), which results when this target is viewed 10 km
from its center at a frequency of 10 GHz. The dynamic range is similar to that of
the simple dumbbell target, but the lobing structure is much more complicated. 3

FIGURE 2.8 Random distribution of 50 scatterers used to obtain Fig. 2.9. See
text for additional details.