Microwave-photonic architecture for direction finding of LPI emitters: post-processing for angle of arrival estimation

Abstract

Direction finding (DF) systems are fundamental electronic support measures for electronic warfare. A number of DF techniques have been developed over the years; however, these systems are limited in bandwidth and resolution and suffer from a complex design for frequency down-conversion. An innovative design of a microwave-photonic direction finding technique for the detection and direction finding of low probability of intercept (LPI) signals is investigated in this thesis. Key advantages of this design include a small baseline, wide bandwidth, high resolution, and minimal space, weight, and power requirement. A unique phase encoding method is used to resolve the ambiguities over the entire field-of-view with high accuracy. Experimental tests using frequency-modulated continuous wave (FMCW) and continuous wave (CW) P4 modulated signals were conducted in an anechoic chamber to verify the system design. Test results showed that the microwave-photonic DF system has a sensitivity of –62.96 dBm and is capable of measuring the angle-of-arrival (AOA) of the LPI signals with <1° resolution over a 180° field-of- view. For an FMCW signal, it was demonstrated that the system is capable of estimating the AOA with a root-mean-square (RMS) error of 0.29° at <1° resolution. For a P4 coded signal, the RMS error in estimating the AOA is 0.32° at 1° resolution.