Radio path length stability of ground-to-ground microwave links
Mark Christopher Thompson · 1964
The Lower Atmosphere PhysicsSection of the National Bureau of Standards, Troposphere and Space Telecommunications Division, conducted a series of eight field experiments in 1958 and 1959 to study the variation in the apparent path length of ground-to- ground microwave links (i.e. , the variations in phase of 9400 Mc/s signals) and the corresponding variations in radio refractive index and other atmospheric parameters measured at the path terminals.This report summarizes the results obtained on paths in Colorado and Florida.It also includes an analysis of long-term variations in the apparent path length and associated variables recorded during each experiment, and a power spectrum analysis of short-term variations in apparent path length and refractivity . 1 .This work was sponsored, in part, by the U. S. Air Force Ballistic Missile Division under contract number AF 04(647) -134.purpose of the experiments was to study the statistical properties of the apparent path length variations and their dependence on various meteorological parameters.The method used for measuring the apparent path length fluctua- tions is basically a phase comparison technique which has been de- scribed previously [Thompson and Vetter, 1958].The most impor- 2 tant atmospheric parameter in this study is the radio refractivity , which was measured in two ways.The long-term variations were obtained from observations of temperature, pressure, and relative humidity.The short-term variations were recorded by the use of a microwave refractometer .Standard meteorological techniques were used to record atmospheric pressure, temperature, relative humidity, wind velocity, and (in some cases) incident solar radiation (insolation) at one or both path terminals.The first of the experiments (referred to hereafter as "runs") was made over a 15. 2 km path near Boulder, Colorado, during a 40 hour period in September 1958.A map and terrain profile of this path are shown in figures 1 and 2. The principal objectives were to study path length variations at 9400 Mc/s over a path having little orno ground reflection, using both horizontal and vertical polarization.The second run, in October, was a continuation of the same type of measurements made in September, but narrower-beam antennas were used and the length of the run was extended to five days to more adequately study day-to-day variations. m1The radio refractivity, N, is defined by N = (n -1) X 10 6 , where n is the radio refractive index.-2-