A Study of a Reactively Loaded Finite Planar Rectangular Waveguide Antenna Array.

An analysis of a general class of antenna arrays, specifically the reactively loaded parasitically excited waveguide-backed aperture antenna array, is presented. The antenna arrays considered have a single waveguide-fed aperture, no complex feed network to all of the apertures, and one reactive load shorted waveguide for each remaining aperture. By varying the position of the short circuits, a directive beam can be steered through 180 deg in space. Only partial control of the array characteristics is possible using this scheme. However, the simplicity of antenna feed design and ease of pattern control makes reactive loading attractive. The antenna arrays investigated have both linear and two dimensional lattices. Each antenna is characterized in terms of power gain, bandwidth, and match. Several examples of magnitude pattern synthesis are presented to show antenna pattern limitations for a given antenna geometry and excitation. In addition, an example using a double-frequency synthesis procedure is given for reshaping gain versus frequency characteristics in the endfire directions. In this direction, gain is higher and bandwidth lower than in other directions. The reactive loading equations for gain and synthesis error are nonlinear equations which normally cannot be solved analytically. Therefore, numerical techniques optimization algorithms are used to find reactive loads for both maximum gain in a specified direction and a synthesized pattern.