TABLE OF CONTENTS A pulse Doppler radar can be ambiguous in either range or Doppler frequency. The ambiguity of a radar depends on the selected PRF. Three modes of airborne radar operation are well known: the high PRF (HPRF), medium PRF (MPRF), and low PRF (LPRF) mode.
In the HPRF mode the PRF is chosen so that the Doppler response is unambiguous for all possible target velocities. As a consequence of the high PRF this mode is usually range ambiguous, that is, the range of a detected target may come either from the indicated range or any range determined by multiples of the PRI. This mode is useful whenever the radial target velocity has to be known unambiguously, for instance in a fighter nose radar in a long range look down situation. In such applications the radial target velocity can be much higher than any relative clutter velocity. In this case the target response appears outside the clutter Doppler band of the radar so that space-time processing is not necessary for clutter rejection.
For the LPRF mode the PRF is chosen so low that the received echoes are unambiguous in range. As a penalty, the Doppler response is ambiguous. The LPRF mode is particularly useful for target search. The MPRF mode is a compromise of the LPRF and HPRF modes and is usually ambiguous in both range and Doppler. For details on the three PRF modes see SCHLEHER [451, pp. 59-73], LACOMME et al. [293].
In the first section of this...
