An Efficient Solution of Phase Interferometry Ambiguity using Zero-Crossing Technique

Abstract

Direction finding systems applying phase interferometer of long baseline gives high accuracy of the angle of arrival measurements; however, they are suffering from phase ambiguity and phase error due to antenna spacing greater than half wavelength of the intercepted signals. In this paper, the simple two-antenna interferometer system has been adopted with the zero-crossing technique used to solve the phase measurement ambiguities in the processing unit. The zeros-crossing of both channels (lead and lag) were extracted using electronic circuitry. A count gate was formed to count the zeros throughout the phase difference between the two channels. The ambiguity factor was taken to be half of the even count which will be added to the output of the phase comparator to estimate the total phase difference. Multisim software has been used to simulate the proposed processing unit and the ambiguity was calculated for different values of phase difference. Antenna spaces (D/λ) of (1/2, 1, 2, 4, 8, 12, 14, and 16) were applied to the system and the corresponding ambiguity factors have been measured to be (zero, 1, 2, 4, 8, 12, 14 and 16) respectively. Therefore for antenna spaces (D ≤ λ/2) there is no ambiguity. These simulated results show a coincidence with the theoretical values. The lead-lag channels were also solved without the need to add other antennas to the system since the first zero detected by either antenna refers to the lead channel. The proposed technique has advantages over others since it solves ambiguities on the basis of real-time processing without the need for complex, expensive, heavy, and slower response systems.