An Interdigitated 3-dB Coupler with Three Strips

An interdigitated microstrip coupler on alumina substrate with three strips and two bond wires is described that provides an alternative to the four-strip Lange coupler. The useful coupling range is between 3 and 6 dB. Experimental results for a 3-dB coupler in the frequency range 4.5-9 GHz are presented together with theoretical results for 3-5-dB coupling.