A Compact Microstrip Branch-Line Coupler with Capacitor Loading

A compact microstrip branch-line coupler with capacitor loading is presented. The new structure not only effectively reduces the occupied area to 33% of the conventional branch-line coupler at 1.0 GHz, but also has high harmonic suppression performance over a wide band. Furthermore, the new structure has only four variable parameters and can be easily designed. The design is validated both by simulation and measurement.