Page 413 - Fundamentals of Radar Signal Processing

TABLE 5.4 Partial List of Advantages and Disadvantages of PRF Regimes for
Airborne Radar

For a given PRF regime, the problem of picking the particular PRFs to be
used remains. Two commonly cited approaches are the “major-minor method”
and the “M-of-N method.” The major-minor method begins by picking at least
two and more likely three “major” PRFs in the regime of interest. The PRFs are
separated by at least the MLC Doppler width ß MLC to guarantee that the first

repetitions of the mainlobe clutter portion of the Doppler spectrum at each PRF
do not overlap, thus making detection presumably possible on at least one of the
PRFs for targets outside of the zero-Doppler clutter region. For each major
PRF, two “minor” PRFs are then selected for use in range ambiguity resolution.
This technique results in sets of six or nine PRFs in total.

The M-of-N method decides how many total PRFs will be used (often eight
in airborne radar) and on how many a detection will be required (usually three).
Any three PRFs on which a detection is observed can be used for range
ambiguity resolution. A variety of techniques have been used to search for sets
that result in good blind zone maps within bounds on the maximum and minimum
PRF; Fig. 5.30 was a particularly good example. A typical ad hoc approach
begins by choosing PRFs that are stepped by at least β MLC /(N – M) Hz. This

choice ensures that the first Doppler blind zones for each PRF do not overlap
for more than N – M PRFs, meaning that any target Doppler shift in that vicinity
will be in the clear on at least M PRFs.
There are some constraints that must be satisfied by the PRFs in either
method. The minimum desired percentage of the Doppler spectrum that is