Phase‐Path Measurements in Space Using Receivers With GPS Clocks

Abstract

A number of new perspectives on wave processes in space may be obtained using a pair of phase-coherent receivers in close proximity to measure the direction of arrival and other parameters of plasma waves. Waves of either spontaneous or artificial origin are of interest. The particular objective of sensing direction is seen as one of several ways to use a measurement of the total phase difference between signals arriving at two receiver sites with a known baseline. The limitations of phase-path measurement using two conventional radio receivers with Global Positioning System (GPS) clocks are investigated. The inherent precision of GPS time means that GPS-based clocks can support useful phase-difference measurements up to at least High Frequency (3-30 MHz). For instance, when receiver separations of hundreds or thousands of meters are permitted, interferometer modes can be envisaged for synchronous detection of natural electromagnetic waves like auroral kilometric radiation or of artificial waves from ground transmitters. The double-heterodyne receiver concept is found to be more accurate than the direct waveform capture type. A rotating double payload comprising two receivers linked by a nonconducting tether, a bolas configuration, is one way to achieve a stable two-receiver direction finder in the ionosphere.