Page 37 - Fundamentals of Radar Signal Processing

processing and because this approach can unify concepts and results often

treated separately.

1.2 Basic Radar Functions

Most uses of radar can be classified as detection, tracking, or imaging. This
text addresses all three, as well as the techniques of signal acquisition and
interference reduction necessary to perform these tasks.
The most fundamental problem in radar is detection of an object or
physical phenomenon. This requires determining whether the receiver output at

a given time represents the echo from a reflecting object or only noise.
Detection decisions are usually made by comparing the amplitude A(t) of the
receiver output (where t represents time) to a threshold T(t), which may be set a
priori in the radar design or may be computed adaptively from the radar data; in
Chap. 6 it will be seen why this detection technique is appropriate. The time
required for a pulse to propagate a distance R and return, thus traveling a total

distance 2R, is just 2R/c; thus, if A(t) > T(t) at some time delay t after a pulse is
0
transmitted, it is assumed that a target is present at range

(1.1)

where c is the speed of light. 1

Once an object has been detected, it may be desirable to track its location
or velocity. A monostatic radar naturally measures position in a spherical
coordinate system with its origin at the radar antenna’s phase center, as shown
i n Fig. 1.1. In this coordinate system, the antenna look direction, sometimes
called the boresight direction, is along the +x axis. The angle θ is called
azimuth angle, while ϕ is called elevation angle. Range R to the object follows
directly from the elapsed time from transmission to detection as just described.
Elevation and azimuth angle ϕ and θ are determined from the antenna

orientation, since the target must normally be in the antenna main beam to be
detected. Velocity is estimated by measuring the Doppler shift of the target
echoes. Doppler shift provides only the radial velocity component, but a series
of measurements of position and radial velocity can be used to infer target
dynamics in all three dimensions.