Page 350 - Fundamentals of Radar Signal Processing

values correspond to PRF = 2667 pulses per second.

FIGURE 5.11 Ambiguity-free range-Doppler coverage regions.

There is some confusion in the terminology regarding the meaning of
“unambiguous velocity” or “unambiguous Doppler shift.” The blind speed
defined in Eq. (5.31) is the velocity interval between zeros of the MTI filter
response. Generally, the range of velocities that are considered to be
measurable without ambiguity is then [–v /2,+v /2]. The unambiguous velocity is
b
b
then said to be v /2 because targets having a velocity magnitude greater than this
b
will be aliased. In terms of Doppler shift, the blind Doppler shift is PRF Hz,
allowing unambiguous measurements over the interval [–PRF/2, + PRF/2]. The
unambiguous Doppler shift is considered to be PRF/2 Hz. However, in some
sources the unambiguous velocity (Doppler shift) is taken to be v m/s (PRF
b
Hz), so caution is needed in interpreting the literature. In this text, unambiguous
velocity or Doppler shift will mean one-half of the first blind velocity or
Doppler shift.
The unambiguous range could be thought of as the range coverage of the
radar for a given PRF while the corresponding blind speed or Doppler could be
considered the velocity or Doppler coverage. Equations (5.30) and (5.31) can
be combined to show that for a given RF and single PRF the combined range-

velocity coverage is a constant, independent of the PRF. The combined range-
Doppler coverage is also independent of the RF: