An eigenmode analysis for a MMW antenna comprised of a periodically-loaded PEC cylinder fed by a dielectric rod

The radiation characteristics of a periodically-loaded perfect electric conductor (PEC) circular cylinder fed by a proximity-coupled dielectric rod waveguide are investigated. The configuration, which is illustrated, is currently being employed as the core radiating mechanism in a host of millimeter-wave (MMW) antenna systems for imaging and communications applications. Several rows of one dimensional gratings are placed along the cylinder axis, each with at slightly differing period, thus allowing for quasi-continuous scanning of the main beam in the E-plane of the antenna. For typical applications, precise control over the scanning behavior and overall radiation characteristics (e.g. beamwidth) is crucial, and as such an analysis tool capable of predicting the performance of the antenna would prove highly beneficial. To this end, we have developed an accurate, analytical formulation for the total radiated fields of the structure based on an eigenmode expansion. Using a cylindrical modal spectrum representation in which a fictitious axial leaky-wave current is impressed on the cylinder surface allows us to model the surface periodicity without the need for a time-consuming full-wave analysis. Several salient features of the antenna´s radiative properties concerning the various geometrical parameters involved are presented.