A Triple-Band Branch-Line Coupler with Simple Structure and Design for WLAN and WiMAX Application

A triple-band branch-line coupler that can operate at two arbitrary frequencies and their mean frequency is proposed. The tripleband operation is achieved by replacing quarter-wavelength impedance transformers in a conventional branch-line coupler by Tshape step impedance transformers comprising two short-circuited stub which can be equivalent to quarter-wavelength impedance transformers at three frequencies. The achieved coupler has simple structure and design process that lead to easily derive the closed-form design equations. For verification, a microstrip ۳ dB branch-line coupler operating at ۲.۳/۳.۷/۵.۱ GHz, covering WLAN and WiMAX frequency bands is designed, fabricated and measured. A Good agreement can be observed between the simulated and measured results.

Keywords:

Branch-line coupler , triple-band , microstrip ,