Rectangular dielectric-rod fed by metallic waveguide

A rectangular dielectric-rod antenna fed by a metallic waveguide is numerically investigated, with emphasis on the mechanism of the gain variation with rod length. Before studying the mechanism, impedance matching between a dielectric rod and a metallic waveguide is performed by introducing a simple technique in which a portion of the rod is inserted into the waveguide. A return loss of greater than 15 dB is obtained over a frequency bandwidth of 11%. The amplitude and phase distributions of the field near the rod are investigated. The field is decomposed into a surface wave propagating along the rod and an unguided wave radiating near the feed end. Calculations show that the phase interaction between the surface and unguided waves occurs near the rod. The gain increase with rod length is explained in terms of the expansion of the equiphase region in the terminal aperture regarded as a secondary Huygens plane