Beam-Forming Capabilities of Waveguide Feeds Assisted by Corrugated Flanges

The physical mechanisms behind the formation of shaped-beam radiation patterns by flat horns (i.e., open ended waveguide feeds with finite-size corrugated flanges) are studied in a rigorous manner using the singular integral equation (SIE) approach. The problem is considered for TM polarization in the two-dimensional (2-D) formulation. First, dispersion curves of periodic grating are presented and used to analyze the modes supported by the waveguide flanges. This includes the surface wave, stopband, and leaky-wave regimes. The modes corresponding to the poles on the bottom “nonphysical” Riemann sheets are also considered. Finally, various types of radiation patterns produced by flat horns with gratings operating in different regimes are illustrated with an emphasis on generating sectoral beams being of interest for many practical applications. The results are validated via comparison with full-wave three-dimensional (3-D) analysis.