Millimeter-Wave Substrate-Integrated Waveguide Multiplexer with High Channel Scalability and High Isolation

This paper proposes a millimeter-wave substrate-integrated waveguide (SIW) multiplexer with high channel scalability and high isolation. To allow flexible increase in the number of channels while reducing the loading effect, a common SIW that is short-circuited at the far end is used to load all channels at locations with maximum magnetic field intensity. Isolation between channels is further improved by staggering higher-order resonances of SIW cavities to suppress any harmonic passband and thus extends the capability of implementing arbitrary passband frequencies. As a proof-of-concept, a quadruplexer was fabricated with center frequencies at 27.1/28.6/37.6/39.3 GHz, where the measured minimum insertion loss is 3.9/3.8/3.6/3.9 dB and the in-band isolation is greater than 37 dB between any two channels. In the frequency range of 20-45 GHz, the measured isolation is greater than 32 dB.