A reduced size planar balun structure for wireless microwave and RF applications

An extremely important component in the realization of certain RF and microwave system topologies is the high frequency balun network. In addition to its application in radiating structures, it has broad utility in numerous wireless communication system topologies. This paper describes a small and compact coupled microstrip line design for use primarily in the exploding portable wireless market. The main advantage of the design to be discussed is that its size is considerably smaller than traditional planar circuit realizations. Size reduction is achieved by utilizing the property of effective length enhancement of a transmission line by employing additive capactive effects. The design technique is illustrated by presentation of computed and measured data on a ~0.9 GHz realization developed for wireless applications