A new class of branch-line directional couplers

A novel class of branch-line coupler is presented in which the shunt transmission line branches of the conventional coupler are replaced by shorted coupled transmission line pairs. This class of couplers allows for the realization of a wider range of designs for both loose coupling and wideband tight coupling values than the conventional coupler. The performance of couplers from this class is comparable to the performance of conventional couplers with only a slight decrease in bandwidth for most designs. Experimental results for a 20-dB microstrip test coupler show measured performance that is very close to predicted performance.<>