Limiting the downward radiation of slanted dipole array

In an attempt to satisfy some government-imposed policies and at the same time optimizing the coverage of an FM antenna system, this paper describes the radiation pattern of the shunt fed slanted dipole, which is the most commonly employed FM broadcast antenna system. The description involves computations of the radiation pattern of an array of slanted dipoles. Free space radiation is assumed in these computations and a simplified model of the antenna structure is used. The basic theory of uniform linear antenna array analysis is first presented. A commercially available simulation and analysis software is used for all gain pattern calculations. Results show that the collective amount of RF signal transmitted by FM broadcast transmitters due to downward radiation using the most common arrangement of slanted dipole array may exceed the maximum permissible amount. By simply varying the distance between identical elements in a uniform linear array used in FM broadcasting, improvements can be done in reducing the downward radiation from minor lobes of the radiation pattern. The areas with reception related problems can also be controlled using this method. However, in reducing the downward radiation of the antenna system, the total gain generally decreases