A design procedure for slitted waveguide leaky wave antennas

An array of leaky waveguides with a single input using an optical chamber (horn) feed, with suitable impedance matching and digital phase-shifters, is one design alternative for sources having waveguide output. The first step in developing such arrays is a flexible design procedure for the individual leaky waveguide elements. The antenna can be phase-scanned by adjusting the propagation constant of the guiding structure and can be frequency-scanned by taking advantage of frequency dispersive behavior. We begin with a design procedure for a variable width aperture in an air-filled rectangular waveguide and show typical radiation patterns. We develop a design procedure for such a leaky waveguide antenna that allows an evaluation of the phase and frequency scan range and radiation pattern characteristics. We then evaluate dielectric loading of rectangular and dual-ridged waveguide as a means to phase scan the main beam position. We present results to demonstrate that voltage controlled dielectric materials can provide phase scanning without corrupting the frequency scan range or radiation pattern. To demonstrate the design we constructed a prototype dual-ridged waveguide with removable dielectric inserts and measured its transmission line and radiation pattern characteristics. To feed and terminate this prototype we were limited to available WR-284 waveguide components and the resulting impedance mismatch is evident in the experimental results. In general the prototype had the expected trends as a function of frequency and dielectric loading. However, an inadequate matched termination of the dual-ridged waveguide led to a large standing-wave-ratio hence a dual beam pattern. We describe some potential applications and make recommendations for further research.