Demonstration of a Wideband Mode Filtering Converter Based on the Four-Ridge Circular Coupling-Cavity Structure

A mode converter (MC) is often used to convert a specific mode into the desired mode, which has been applied to various electromagnetic systems, while the conventional MC design mainly focuses on conversion efficiency, operating bandwidth, and size but often ignores the sideband performance. As a result, the unwanted modes and frequencies near the sideband may sneak into the system and lead to instability. Here, based on the four-ridge circular coupling-cavity structure (FCCS), we propose a wideband mode filtering converter (MFC) that can be regarded as an integration of an MC, a frequency filter, and a mode filter due to the high mode purity in the passband and out-of-band rejection characteristics, as well as the mode filtering performance. Furthermore, an X-band wideband TE10to TM01MFC was fabricated and tested. The experimental results are in good agreement with the simulation results and also indicate that MFCs possess both the out-of-band rejection and mode filtering characteristics.