Phase Coherent EM Array Measurements in a Refractive Environment

Phase-coherent measurements of the pilot tone from a digital television (DTV) station were taken by a 24-element vertical array 168 km from the transmitter. Measurements were recorded over 15 days in Southern California, a region known for ducting events in which abnormal atmospheric refractivity patterns allow for the exceptionally long-range propagation of electromagnetic (EM) waves. The DTV station was positioned over the horizon (OTH) relative to the receiver array such that the line of sight was obstructed; thus, significant diffraction loss was expected. Direction-of-arrival (DOA) estimation was performed on the measurements. The measurement campaign objective was to collect the first long-term data set of DOA and the array-signal-to-noise ratio (ASNR) from signals propagating OTH through a refractive channel, toward the goal of enhancing the fidelity of atmospheric refractivity estimates. The analysis of the collected data shows that ASNR is correlated with atmospheric parameters related to refractivity.