FM wide band panel dipole antenna

Abstract

It is very common that when a broadcaster needs to install an FM transmitting antenna within a large metropolitan area he places it on the tallest structure or building available. When the rooftop is already occupied by a large number of other types of transmitting and receiving antennas, the panel dipole antenna should be chosen. This antenna is secured to the side walls of the upper floors with the panel oriented to obtain full coverage of the most desirable areas of the city. For the Buenos Aires area this orientation avoids radiating toward Uruguay and specifically toward Montevideo, some 140 miles away. A wide band antenna operation permits placing the station on the air and at the same time allows future stations to share it without the installation of new antennas. Details of model and full model impedance and radiation pattern measurements during the antenna development are presented in order to show its technical characteristics. The radiation patterns were measured on a scale model in an anechoic chamber. The full scaled model was measured in an outdoor antenna range. Both E and H plane radiation patterns were measured along the FM band in order to observe pattern variations on both planes. Practically no difference in a panel radiation beamwidth from 88 to 108 MHz was observed and at the same time good input impedance was maintained. A really wide band antenna in pattern and VSWR is obtained. Power division for the antenna system is obtained designing an eight port power divider using the microstrip line technique. In this case, however due to high power operation the ground plane and strip are contained in a sealed metallic box and are separated by high pressure dry air like into the 3" feeding coaxial line.