Page 71 - Fundamentals of Radar Signal Processing

example via Doppler processing or synthetic aperture radar (SAR) imaging,

are said to form a coherent processing interval (CPI). A still higher level of
radar processing acts on data from multiple CPIs and therefore operates on an
even longer time scale often called a dwell and typically lasting milliseconds to
ones or tens of seconds. Operations on this scale include multiple-CPI detection
and ambiguity resolution techniques, multilook SAR imaging, and track filtering.
Some radars may track detected targets for many seconds or minutes using data

from multiple dwells. Track filtering operates in this regime. Finally, some
imaging radars may monitor an area over days, months, or even years.

1.5.2 Phenomenology
To design a successful signal processor, the nature of the signals to be
processed must be understood. Phenomenology refers to the characteristics of
the signals received by the radar. Relevant characteristics include signal power,
frequency, phase, polarization, or angle of arrival; variation in time and spatial

location; and randomness. The received signal phenomenology is determined by
both intrinsic features of the physical object(s) giving rise to the radar echo,
such as their physical size or their orientation and velocity relative to the radar;
and the characteristics of the radar itself such as its transmitted waveform,
polarization, or antenna gain. For example, if more power is transmitted a more
powerful received echo is expected, all other things being equal.

In Chap. 2, models of the behavior of typical measured signals that are
relevant to the design of signal processors are developed. The radar range
equation will give a means of predicting signal power. The Doppler
phenomenon will predict received frequency. It will be seen that the complexity
of the real world gives rise to very complex variations in radar signals; this will
lead to the use of random processes to model the signals, and to particular
probability density functions that match measured behavior well. A (very) brief

overview of the behavior of the variation of ground and sea echo with sensing
geometry and radar characteristics will be given. It will also be shown that
measured signals can be represented as the convolution of the “true” signal
representing the ideal measurement with the radar waveform (in the range
dimension) or its antenna pattern (in the azimuth or elevation dimension, both
also called cross-range dimension). Thus, a combination of random process and

linear systems theory will be used to describe radar signals and to design and
analyze radar signal processors.

1.5.3 Signal Conditioning and Interference Suppression
The first several blocks after the antenna in Fig. 1.18 can be considered as
signal conditioning operations whose purpose is to improve the SIR of the data
prior to detection, parameter measurement, or imaging operations. That is, the
intent of these blocks is to “clean up” the radar data as much as possible. This is

done in general with a combination of fixed and adaptive beamforming, pulse