New angle-of-arrival measurement technique for over ocean propagation studies

Abstract

Radio propagation experiments are a useful tool when verifying propagation models and identifying anomalies in a practical link. This paper describes a new method to measure the Angle-of-Arrival (AoA) of a radio signal for terrestrial propagation studies. The new technique allows the phase of radio signals received by incoherent detectors arranged in an array formation to be obtained. This measurement, along with the amplitude readings at each element of the array can then be processed to find the AoA of signals on the array. The proposed technique is novel in that frequency drift and offsets, arising because the different receivers are incoherent, are compensated for by way of a common reference signal injected into the front of the array. The phase of the incoming signals are obtained by processing the down-converted and digitized waveforms. A novel approach based on an adaptive, discrete-time quadrature delay estimator (QDE) algorithm is used for this purpose. This algorithm is insensitive to variations in the amplitudes of the input signals, and does not require an accurate prior estimate of the frequency of the input sinusoids. This approach is shown to be an accurate, low cost alternative to conventional vector measurement techniques when used with large antenna arrays and is therefore well suited to fixed link, angle-of-arrival measurements.