Design and Testing of a Feed Network for a Transparent Antenna Array

This paper describes the design and testing of a feed network for a transparent flat plate array antenna. This antenna is the top of a stack of three antennas that must occupy the same volume while pointing in different directions. At many pointing angles, the antenna will create blockage for the antennas underneath. In order to minimize the blockage, the array and its transmission lines must be as transparent as possible to the antennas underneath. The flat plate array consists of active elements over a frequency selective surface (FSS) ground plane that is transparent at the frequencies of the antennas below. The feed lines must also be transparent to the antennas below. This is achieved by minimizing the total area occupied by the feed lines. Rather than the traditional corporate feed network, a series feed network was designed. Such a network requires that each individual feed point must be fed with a coupler where the coupling coefficient is adjusted to distribute the same power to each array element. We will show the details of the design of the network as well as a set of measurements that show the performance.