An Improved Multi-Layer Quadrature Coupler for MMICs

A novel technique for significantly reducing the insertion loss of multi-layer quadrature couplers is presented. With previous broadside multi-layer couplers, realized on GaAs MMICs, the upper conducting layer track is overlayed exactly onto the much thinner lower conducting layer track - resulting in a high insertion loss. A new multi-layer structure is presented that has an upper track which is offset - so that the lower track can be plated-up with the much thicker metal from the upper track, thus, reducing the even-mode insertion loss. A coupler, with a centre frequency of 7.7GHz, incorporating this technique has been realized on a GaAs MMIC, with maximum dimensions of only 1.l×0.8mm. The resulting insertion loss at centre frequency is less than 1dB. The overall performance has been found to equally match that of the Lange coupler.