Radiation pattern shaping for FM broadcast-optimizing coverage

Abstract

This paper describes how to configure the radiation pattern of an omnidirectional FM antenna to at least approximate a desired directional radiation pattern. The desired radiation pattern is based on the population location within the coverage area of an FM radio station. In this way, the station will transmit signal only in directions where the signal is needed, thereby the station's transmitter will be operating at much reduced power. A linear uniform antenna array is used to produce the customized radiation pattern on the horizontal plane. The array is composed of two basic identical omnidirectional antennas, each is called a bay. By determining the proper distance and phase relationship of the two identical basic antennas, any radiation pattern can be realized. Genetic algorithm (GA) is used in optimizing the values of the distance and the phase relationship of the two bays in linear array, producing an optimized radiation pattern identical to the desired radiation pattern. Genetic Algorithm is implemented in Matlab. Optimum values of the GA parameters are first determined prior to the optimization of the radiation pattern for a more accurate, consistent and faster results. Two directional patterns are presented to demonstrate the method. Finally, an antenna simulation software is used to validate the results in each case.