A Compact Wideband Diplexer Covering X- and Ku-Bands with Enhanced Higher-Order Mode Suppression

This paper presents a design of an E-plane wideband diplexer that boasts a full fractional bandwidth of about 60 % with an enhanced suppression of higher order modes. The proposed design overcomes the challenging problem of suppressing TE20 and TE01 modes in very wideband diplexers. The design introduces a very broadband ridge waveguide E-plane duplexing junction that allows only modes with even electromagnetic symmetry to propagate in this wide bandwidth. The diplexer utilizes ridge waveguide lowpass and bandpass filters for the two channels. Transitions from the custom ridge waveguide ports to standard WR90 and WR62 ports are incorporated in the design. This yields a diplexer with standard rectangular ports that may eventually support higher order modes, but with a duplexing core that suppresses them. The design is discussed in detail followed by an experimental prototype which was fabricated and tested demonstrating good results without any tuning.