Balanced Diplexer Based on Substrate Integrated Waveguide Dual-Mode Resonator

Abstract

This article presents a novel balanced diplexer based on substrate integrated waveguide (SIW) dual-mode resonator. The six-port model has been introduced in this article to achieve the conversion of S-parameters between balanced and unbalanced devices. The SIW dual-mode resonator with common-mode (CM) rejection capability is able to restrain CM signal in the passband of the diplexer. Moreover, the CM rejection performance is improved by etching the slotline on the surface of SIW without changing the transmission of the differential-mode (DM) signal. A diplexer with lower and higher channels centered at 8.8 and 9.4 GHz, with a 3-dB FBW of 4% and 4.8%, respectively, is designed and fabricated to verify the proposed concept. The measured results show that the CM rejection is greater than 42/45 dB and the DM isolation between the lower and higher channels is greater than 35 dB in passband, which shows good agreements with simulations.