Page 70 - Fundamentals of Radar Signal Processing

FIGURE 1.19 Illustration of the range of time scales over which radar signal
processing is performed.

Operations that are applied to data from a single pulse occur on the
shortest time scale, often referred to as fast time because the sample rate,
determined by the instantaneous pulse bandwidth (see Chap. 2), is on the order
of hundreds of kilohertz (kHz) to as much as a few gigahertz in some cases.

Corresponding sampling intervals range from a few microseconds down to a
fraction of a nanosecond, and signal processing operations on these samples
therefore tend to act over similar time intervals. Typical fast time operations are
digital I/Q signal formation, beamforming, pulse compression or matched
filtering, and sensitivity time control.
The next level up in signal processing operations operates on data from
multiple pulses. The sampling interval between pulses (the PRI) is typically on

the order of tens of microseconds to hundreds of milliseconds, so again
operations that involve multiple pulses occupy similar time scales. Due to the
much slower sampling rate compared to single-pulse operations, such
operations are said to act in slow time. Typical operations include coherent and
noncoherent integration, Doppler processing of all types, synthetic aperture
imaging, and space-time adaptive processing. The idea of slow and fast time

will be revisited in the discussion of the data organizational concept of the
datacube in Chap. 3.
A group of pulses that are to be somehow combined coherently, for