Abstract:In the design of wide-band Marchand Balun，the three-conductor coupled lines which replace the two-conductor coupled lines were adopted to broaden the bandwidth and enhance the coupling factor. The capacitance，inductance compensation and impedance network were utilized to improve port match performance. Simulation results show that the port match，output balance and phase differences have been improved．Between the bandwidth from 20 GHz to 55 GHz，S22,S33 are both smaller than -15 dB, while S23,S21 are smaller than -10 dB and -3.6 dB respectively. The amplitude difference is about 0.1 dB.