Tunable SIW Cavity-Based Dual-Mode Diplexers With Various Single-Ended and Balanced Ports

This paper presents, for the first time, tunable dual-mode substrate integrated waveguide (SIW) diplexers with various single-ended (SE) or balanced (BAL) ports. Dual-mode diplexing reduces the required volume by half while signal routing is achieved by proper coupling sections. Furthermore, the SIW resonators result in low loss and wide tunability. This paper experimentally demonstrates three designs with SE–SE, SE–BAL, and BAL–BAL port configurations. The SE–SE, SE–BAL, and BAL–BAL diplexers can be tuned starting from 2.07, 2.2, and 2 GHz, respectively, with a tuning range of 45%, 57.2%, and 63.5%, respectively. The average measured insertion loss is 1.32 dB for the SE–SE, 1.95 dB for the SE–BAL, and 2.15 dB for the BAL–BAL. The average size of the diplexer is
$55{\times} 55$
mm
²
. For the proposed SE–BAL and BAL–BAL diplexers, the measured in-band common-mode rejection is better than 40 dB throughout the tuning range.