Design of Wide Passband Microstrip Branch-Line Couplers With Multiple Sections

Novel design equations are proposed for the 3-dB microstrip branch-line coupler with a wide passband, utilizing multisectional branch lines. In addition, the proposed method makes it possible to reduce the internal impedance levels of branch-line couplers so they may be physically constructed by microstrip lines. Further, in terms of measured results, there is a wide bandwidth >70%. Synthesis of the 3-dB branch-line coupler is described in details as well. Good agreement between theoretical calculation and measurement validates the proposed method.