B.S.T.J. Briefs: Low-Elevation-Angle Propagation Effects on COMSTAR Satellite Signals

Low-Elevation-Angle Propagation Effects on COMSTAR Satellite Signals By J. M. TITUS* and H. W. ARNOLD (Manuscript received April 30, 1982) I. INTRODUCTION Little information exists on earth-space propagation at lower elevation angles. One earlier experiment 1 has shown greater fluctuation in signal levels over low-elevation paths. This signal fluctuation likely results from focusing and defocusing by inhomogeneities in the atmosphere's index of refraction caused by turbulence. T h e f l u c t u a t i o n increases at lower elevation angles, then, because the signal must pass through more atmosphere. The opportunity existed during 1976 to make more low-elevation observations at 19 GHz as the COMSTAR satellites were placed into position. This paper describes the acquisition and analysis of the lowelevation propagation data. Results are presented showing the fluctuation intensity of the received signal at several elevation angles. II. EXPERIMENT Two satellites were launched carrying 19-GHz beacon transmitters, in May 1976, and COMSTAR II in June 1976. As they were placed in their final positions, they drifted upward from the horizon at a rate of 1 to 2 degrees per day. Original data were taken at 19 GHz on Crawford Hill for elevation angles from 1 to 10 degrees above the horizon with a 3.7-meter diameter antenna and an interim receiver. 2 Signals received on vertical and horizontal polarizations (relative to the Crawford Hill horizon) were recorded on analog magnetic tape. COMSTAR I * This work was performed while Ms.