Compact and broad-band three-dimensional MMIC balun

This paper presents a simple and effective technique,which compensates for the amplitude and phase differences of the Marchand balun. Compensation is accomplished by interconnecting a short transmission line to a pair of couplers. As a result, Marchand balun with operation frequency ranging as wide as 8.2-30 GHz is achieved. To fabricate the prototype, we adopt three-dimensional monolithic-microwave integrated-circuit technology together with a 2.5 mu m x 4 layer polyimide structure stacked over a GaAs wafer. The topology yields a circuit area as small as 0.2 mm x 0.4 mm for the balun.