Unified Microwave Terahertz Waveguide Coupler for Multiband Wireless Applications

In this work, a microwave and terahertz (THz) composite waveguide coupler for multiband wireless systems is proposed and demonstrated. Such a very large frequency ratio (more than twenty times) of the proposed coupler is made possible thanks to a composite waveguide technique where the center strip of a coplanar waveguide (CPW) is replaced by a substrate-integrated waveguide (SIW) block. In this way, the dual-mode operation, i.e., quasi-TEM mode and TE₁₀ mode, can be enabled simultaneously at different frequencies. In addition, by adjusting the SIW width, operating frequency of the quasi-TEM mode and the TE10 mode can be reassigned. All the advantages known for CPW couplers and SIW couplers are inherited in the proposed waveguide coupler. To validate this scheme, experimental prototypes are developed and fabricated on a thin-film miniature hybrid microwave integrated circuit (MHMIC) process. Measured results confirm the good THz performance as well as microwave performance.