A Novel Broadband Even-Mode Matching Network for Marchand Baluns

In this paper, we present the development of an even-mode matching network for a Marchand balun to achieve 50-?? match and high isolation at the balanced ports. A very wide matching bandwidth can be accomplished with the novel addition of an open-circuit stub to the network. Experimental results demonstrate that the even-mode matched balun achieves return losses that are greater than 15 dB at the balanced ports from 6 to 17 GHz. The measured isolation between the balanced ports is greater than 15 dB from 4 to 19 GHz. For the unbalanced port, the return loss is greater than 15 dB from 4 to 19 GHz. The measured insertion loss is less than 1 dB, and amplitude and phase imbalances are ??0.5 dB and ??5?? from 4 to 18 GHz, respectively.