Compact 2-step Septulum Polarization Converters for Radars and Satellite Systems

This article presents the results of analysis, numerical simulations and optimization of new narrowband guide septulum polarization converters. Orthomode duplexers and polarization converter designs based on septulums are widely used in modern microwave systems with orthogonal circularly polarized signals. Septulum guide polarizer is an effective compact device, which transforms right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic modes into linearly polarized ones. At the same time it divides RHCP and LHCP modes and directs them to two different rectangular guides with high signal discrimination to each other. Thus, a septulum-based guide device integrates performance of a polarization transformer and of an orthomode duplexer. The main electromagnetic characteristics of the polarization converter were simulated in software based on the finite elements method in the frequency domain. The proposed design of a compact narrowband guide polarization converter has a septulum with two steps. Several designs of septulum polarization converters were developed and compared for different relative bandwidths of 5%, 10%, and 15%. The comparative investigation of the obtained designs was carried out. Main electromagnetic characteristics of optimal septulum polarization converters were compared. These include return losses, cross-polarization discrimination, ellipticity parameter, and ports discrimination. It was demonstrated that in 5% fractional bandwidth a compact 2-stepped septulum polarization converter has return losses greater than 22 dB. Its cross-polarization discrimination and ports discrimination are greater than 25 and 27 dB. Developed compact septulum polarization converters can be applied in modern antenna systems for radars and satellite communication systems.