Description of Computer Program to Analyze Gain Distribution of an Antenna Pattern

Abstract

The gain of a radiating antenna is generally a function of the direction in which the antenna is pointing relative to the direction of the received or transmitted signal. The gain distribution over an imaginary sphere surrounding the antenna is called the antenna gain pattern and can be measured experimentally. Under certain circumstances the tolerances associated with the pointing vector make it impossible to determine the antenna gain precisely but rather circumscribe an area on the spherical surface which include a number of different gain values. A computer program called INTGRT has been developed that will determine from measured antenna pattern data the gain distribution within the uncertainty region and will provide a measure of the probability of the gain being above a certain gain value. The boundary of the uncertainty region is described in terms of the coordinate system used in measuring the antenna patterns. Each gain value contained inside this boundary is compared to some reference gain level and a running total is made of the number of values found to be equal to or greater than the reference value and the total number of values inside the region. After weighting each total by an equal area function, the ratio of the number of values above a reference level to the total number of values in the region gives an estimate of the probability that the gain of the antenna will be equal to or above the reference gain. If the region is analyzed in this way for a number of reference levels, the distribution of gain values within the region is obtained. This information is extremely valuable in determining space communication system performance during periods in which the orientation of the spacecraft's antenna with respect to the earth cannot be determined precisely but is known to be within certain limits.