A new class of dielectric-loaded hybrid-mode horn antennas with selective gain: design and analysis by single mode model and method of moments

A mechanically simple dielectric loaded hybrid mode horn is presented. It can be designed to satisfy either hard or soft boundary conditions, or any boundary between hard and soft under balanced hybrid condition (low cross-polarization) for any aperture size. Design curves are developed based on a plane wave model. Radiation performance is computed based on a single mode circular cylindrical wave model (CCWM) as well as by method of moments (MoM). Based on CCWM aperture efficiency of about 94% has been computed at the design frequency for a 3.38λ aperture with hard boundary condition and a dielectric constant of 4.0. The same horn with a dielectric constant of 2.5 can provide higher than 89% aperture efficiency and under -30 dB cross-polarization over a 15% frequency range. Predicted peak sidelobes ranging from -19 to -26.5 dB and corresponding aperture efficiency between 92% and 78% at the design frequency under balanced hybrid condition have been obtained for various horn designs. Computations based on MoM show that cross-polarization patterns agree well with what was predicted based on an ideal single hybrid-mode model, while computed aperture efficiency is even higher than predicted by CCWM. Results also indicate that implementing dielectric-to-air matching at the horn aperture is crucial to achieve good cross-polarization performance and input match for hard horns in general. The horn can also be designed to radiate a flat-top pattern. The horn could be useful as an element in cluster feeds or limited-scan arrays, as a feed for quasioptical amplifier arrays or in millimeter wave applications.