Design of a new class of microwave biasing networks with modal-matching properties

A new four-port microwave-biasing network with modal-matching properties is presented. The new network can be used to bias differential circuits and has a high common-mode rejection ratio, which is frequency-independent. It is comprised of a pair of Marchand baluns intermediated by a filtering stage with an overall physical size that can be predetermined as a design parameter. The design procedure is based on the exact synthesis of a filter prototype with a prescribed set of transmission zeros. The new network was implemented on a printed circuit board and used to bias a pseudo-differential amplifier. The measured performance of the sub-system configuration demonstrated low common-mode gain over a broad bandwidth as theoretically predicted.