Page 78 - Fundamentals of Radar Signal Processing

FIGURE 1.23 The concept of synthetic aperture radar.

1.5.5 Detection
The most basic function of a radar signal processor is detection of the presence
of one or more targets of interest. Information about the presence of targets is
contained in the echoes of the radar pulses. These echoes compete with receiver

noise, undesired echoes from clutter signals, and possibly intentional or
unintentional jamming. The signal processor must somehow analyze the total
received signal and determine whether it contains a desirable target echo and, if
so, at what range, angle, and velocity.
Because the complexity of radar signals leads to the use of statistical
models, detection of target echoes in the presence of competing interference

signals is a problem in statistical decision theory. The theory as applied to radar
detection will be developed in Chap. 6. There it will be seen that in most cases
optimal performance can be obtained using threshold detection. In this method,
the magnitude of each complex sample of the radar echo signal, possibly after
signal conditioning and interference suppression, is compared to a precomputed
threshold. If the signal amplitude is below the threshold, it is assumed to be due
to interference signals only. If it is above the threshold, it is assumed that the

stronger signal is due to the presence of a target echo in addition to the
interference, and a detection or “hit” is declared. In essence, the detector makes
a decision as to whether the energy in each received signal sample is too large
to likely have resulted from interference alone; if so, it is assumed a target echo
contributed to that sample. Figure 1.24 illustrates the concept. The “clutter +
target” signal might represent the variation in received signal strength versus