Introduction - Time-Frequency Transforms for Radar Imaging and Signal Analysis - page 2

Figure 1.1 Radar operational scenario.

where R is the range from the radar to the target and c is the speed of
electromagnetic wave propagation.
When the target is moving with a velocity V R relative to the radar,
called the radial velocity, the radar signal must travel a longer or shorter
distance to reach the target. The signal received at time t is reflected from
the target at time ( t - t ( t )/ 2 ), and the round-trip travel time is a time-

varying delay t ( t ).
In addition to the signal reflected from the target, there is also additive
noise. The signal-to-noise ratio (SNR) at the radar receiver is determined
by the intensity of the received signal, the noise figure, and bandwidth of
the receiver. Any improvement in SNR will increase the probability of the
target detection and the accuracy of parameter estimation.
Radar usually transmits a sequence of pulses or other signal waveforms
at a pulse repetition frequency (PRF) required by the maximum range of
detection. In the radar receiver, the received RF signal is first converted to
an intermediate frequency (IF) signal. Then, the IF signal is converted into
two video frequency signals, the in-phase and the quadrature-phase (I and
Q) components, using two synchronous detectors that have an identical
reference signal but 90-degree phase difference between them. The I and Q
signals can preserve the phase information contained in the IF signal and,
thus, enable the positive and the negative Doppler frequency shift to be
distinguished [1-3].
Target information embedded in the returned signals may be examined
directly from the radar range profile [i.e., the distribution of target reflectivity
along the radar line of sight (LOS) to the target] or from its frequency