Analysis and Design of Flange-Integrated Rectangular-To-Circular Waveguide Transformers for Splashplate Antenna Feeds

A new design concept for compact rectangular-to-circular waveguide transformer is presented. It allows the integration of the transformer in the flange of a circular waveguide splashplate feed. Instead of using a conventional taper, short and abruptly stepped rectangular and circular transformer sections are utilized. Two different designs are presented which achieve 30dB-return-loss bandwidths of 12 and 19 percent. The corresponding component lengths are only 0.71 and 1.1 guided wavelengths, respectively, at the center frequency of the rectangular input waveguide. The design methodology is validated by excellent agreement between theoretical predictions, HFSS analyses and measurements.