Compact high directivity branch‐line hybrid using distributed realization of lumped elements

Abstract

AbstractThis letter presents a compact high directivity branch‐line hybrid. The proposed hybrid is designed using a symmetrical ‐shaped structure, which incorporates a symmetrical ‐equivalent circuit. The ‐structure comprises one series low‐impedance line and two shunt high‐impedance stubs. The low‐impedance line is realized using a ‐equivalent circuit consisting of two spiral inductors and one patch capacitor. A detailed analytical design procedure is developed. A prototype hybrid is fabricated on FR‐4 substrate and the measured ‐parameters are in close agreement with the simulated results. The proposed hybrid has a compact size with 54% area reduction compared to a conventional branch‐line hybrid. In addition, the hybrid achieves 43 dB directivity at its center frequency of 0.9 GHz.