Wideband branch line coupler with arbitrary coupling ratio

In this paper, we introduce a design method for wideband branch line couplers with an arbitrary power coupling ratio. The design method is based on a matching condition for a wideband and the arbitrary coupling. The coupler has been constructed by connecting four capacitively coupled λ/4 open circuited lines directly to every input port and by adopting proper characteristic impedances for arbitrary power coupling. Three couplers 5-dB, 8-dB, and 10-dB have been simulated, fabricated, and measured. The simulated and measured results are compared. A fractional bandwidth up to 63% with very flat characteristics for the condition of a 20 dB return loss has been measured for the case of the 10-dB coupler. The couplers have been developed in a suspended microstrip and microstrip line structures.