Orthogonal-polarization multipulse sequences

Abstract

It is well known that using orthogonal polarizations for subpulses in multipulse sequences can be used to reduce clutter contributions in these modes. In this paper we show that further improvements are achieved if the orthogonality is taken into account already when constructing the codes. Using orthogonal polarizations, one can use denser transmission patterns, including elementary pulses without gaps between them, patterns that have severe range ambiguities when only a single polarization is used. Furthermore, correlations are computed separately for each combination of elementary pulse polarizations. Consequently, it is possible to have longer multipulse sequences without gaps in the lag sequence, it is possible to compute the odd lags as well as the even ones, and it is permissible to have some lags multiply obtained without range ambiguity. This means that using orthogonal polarizations when creating the multipulse transmission pattern gives flexibility well beyond the single-polarization case. This flexibility can be used to design patterns suited to particular experimental requirements. Furthermore, we point out that the improvement in clutter might have a more dramatic impact than is generally realized, particularly in high-SNR situations where the improvement in speed is up to a factor of 4. Examples are given of single- and multiple-frequency patterns that are not usable if only one polarization is available. Although all incoherent scatter radars in use today, except Jicamarca, lack orthogonal polarization capabilities, designers of the next generation of radars might find the improvements described herein to be of interest. Copyright 2011 by the American Geophysical Union.