Digital polarimetric system

Abstract

A digital polarimeteric system employs a signal time stretching technique and digital signal processing of the time-stretched signal to accurately measure the polarization of a received RF signal with commercially available digital hardware. A superheterodyne receiver down converts received RF signal components to IF, and analog-to-digital converters sample the signal components at much lower sampling rates than would normally be required to accurately measure the signal polarization. Each signal sample is 'time stretched' by storing each sample in M locations in a memory, such that N samples occupy M×N memory locations. A digital signal processor applies incremental phase shifts to the digital samples until a phase-shifted combination of the digital samples yields a minimum null output. The phase shifts producing the minimum null identify the polarization of the received signal. The stretching and digital processing yield the required number of samples per cycle of the received signal for accurate polarization measurement, thus effectively increasing the digital sampling frequency. Because each sample is stored in M memory locations, each incremental phase shift corresponds to 1/Mof the actual sampling interval, thereby providing the high phase resolution required to accurately measure polarization.