Compact Microstrip Dual-Band Quadrature Coupler Based on Coupled-Resonator Technique

A compact dual-band coupled-resonator quadrature (90°) coupler with flexible passband allocation has been presented. By introducing the dual coupling paths between input and output ports, the design flexibility is increased, and thus, a dual-band response can be realized. For demonstration, a dual-band 90° coupler operating at 1.6 and 2.1 GHz has been designed and fabricated with microstrip technology. The 90° coupler is formed by only four dual-mode stub-loaded resonators, leading to a compact size, i.e., about 0.27 λg by 0.27 λg. A good agreement is achieved between simulation and measurement.