E-Plane Waveguide Filtering Six-Port Junction

A novel E-plane filtering six-port junction (SPJ) based on waveguide is presented. Different from the traditional designs, the proposed SPJ is formed by two identical filtering 180 degrees couplers and two waveguide couplers with 180 degrees and 90 degrees phase shifts. A coupling-matrix (CM) technique, combining both resonant and nonresonant structures, has been developed to represent the entire SPJ. This has been used to predict the theoretical response as well as to investigate the effect of the couplers on the performance of the SPJ. A demonstrator has been designed to work at 10 GHz with a bandwidth of 0.4 GHz. Stub-loaded waveguide resonators have been used to keep a consistent profile and ease the layout of the complicated waveguide network. A good agreement between the CM-based theoretical responses, simulations, and measurement has been achieved. The measured average insertion loss is 0.4 dB, and the maximum in-band phase error is 10 degrees. The measured in-band isolation between two input ports is higher than 26 dB.