A Simple Dual-Band Coupler Design Based on A Novel Dual-Mode Transmission Line Structure

A simple dual-band coupler design method based on a novel type of dual-mode transmission line is presented. The electric field distributions of different modes of the transmission line are studied, based on which the feasibility of the dual-band joint design method is explained. In particular, the phase and impedance conditions of the coupler are analyzed, and related parameters can be controlled to meet the design requirements of the dual-band coupler. In addition, a slow-wave structure is used to control the frequency ratio more flexibly. A dual-band coupler example centered at 22 and 30 GHz is designed and demonstrated as a proof of concept. The simulated results show satisfactory matching performance and phase imbalance in both bands.