Page 193 - Fundamentals of Radar Signal Processing

FIGURE 3.8 Datacube illustrating one CPI of data from a multichannel pulsed
radar.

How large is a datacube? The number of samples in each dimension are
determined by the characteristics of the desired radar measurements. The
number L of range samples is simply the length of the range swath divided by
the range bin spacing, L = R /ΔR . The swath length is determined by mission
w
s
requirements, while the range bin spacing is determined primarily by the
waveform bandwidth as seen in Eq. (3.1). Both may vary significantly for the

same radar as it switches between various operating modes with different
search ranges and range resolutions.
One important determinant of the number of pulses M in a CPI is the
desired Doppler resolution (equivalently, velocity resolution). The Doppler
spectrum is the DTFT of the slow-time data. The duration of the slow-time
signal is the CPI length of MT seconds. The Doppler resolution will therefore
5
be on the order of ΔF = 1/MT, giving the required number of pulses as M =
D
1/ΔF T = PRF/ΔF . Thus, M depends on the PRF as well as the Doppler
D
D
resolution, and can vary widely. In pulse-Doppler processing for basic target
detection and tracking, M is frequently a small number of tens of pulses.
However, in fine-resolution imaging it can be hundreds or even thousands of
pulses.

For a multichannel receiver, the number N of channels is more difficult to
characterize. A phased array antenna with a receiver per element may have
hundreds or thousands of phase centers, each constituting a receiver channel. A
subarrayed architecture may have many fewer, perhaps ranging from as little as
three or four to a few tens. A monopulse antenna has three phase centers. The
antenna type, size, and architecture all significantly influence N.
The datacube view of a CPI of data from a multichannel pulsed radar

provides a good conceptual model for understanding most digital radar signal
processing operations. Many of the basic radar signal processing operations
considered in the remainder of this text correspond to processing one-