Compact Dual-Band Branch-Line Coupler With Dual Transmission Lines

Abstract

This letter presents a dual-band branch-line coupler with compact size and planar structure. The π-shaped dual transmission lines structure is used to realize 90° phase shift at two arbitrary frequencies. Explicit design equations are derived using the ABCD and admittance matrices. For verification, a prototype is designed, fabricated, and tested. The coupler has a compact size with 76% size reduction compared with the conventional circuit at the first band. The measured results are in good agreement with the simulated results.