Page 147 - Fundamentals of Radar Signal Processing

techniques such as matched filtering and Doppler processing.

Like Eq. (2.11), Eq. (2.85) is also often called the radar range equation. In
the remainder of this text, the term “range equation” or “radar range equation”
usually refers to the SNR form of Eq. (2.85) and its analogues for volume and
area scatterers.

2.5 Jamming
Jamming refers to intentional interference directed at the radar system from a
hostile emitter. Jamming is an example of electronic countermeasures (ECM)

or electronic attack (EA). As noted earlier, the purpose of most radar signal
processing is to improve the SIR of the data so as to improve detection,
tracking, and imaging performance. The purpose of many jamming techniques is
just the opposite: to reduce the SIR so that the radar performance is degraded.
The most basic form of jamming is simple noise jamming. A hostile emitter
directs an amplified noise waveform at the victim radar, essentially increasing

the noise level out of the receiver. If the noise power spectrum fills the entire
radar receiver bandwidth, then the noise out of the receiver will appear like any
other white noise process and is modeled in the same way. More advanced
forms of noise jamming use various amplitude and frequency modulations.
Instead of noise, other jamming techniques use waveforms designed to mimic
target echoes and fool the radar into detecting and tracking nonexistent targets.
Even a limited discussion of ECM is outside the scope of this text, due

both to the breadth of the topic and the limited amount of material publishable in
the open literature. The reader is referred to Lothes et al. (1990) for a good
general reference on jamming signals in radar.

2.6 Frequency Models: The Doppler Shift

2.6.1 Doppler Shift
If the radar and scatterer are not at rest with respect to each other, the frequency
F of the received echo will differ from the transmitted frequency F due to the
r
t
Doppler effect. Doppler shifts can be used to advantage to detect echoes from
moving targets in the presence of much stronger echoes from clutter or to
drastically improve cross-range resolution. Uncompensated Doppler shifts can
also have harmful effects, particularly a loss of sensitivity for some types of
waveforms. Thus, characterization and measurement of Doppler shifts is an
important topic in radar.

Consider an arbitrary waveform x(t), pulsed or not, transmitted by a
monostatic radar. The waveform is reflected from a perfectly conducting target
at an arbitrarily time-varying range R(t). For instance, a constant-range target