Balun based on a log-periodic phase shifter

The log-periodic principle of antennas can be applied to circuits with guided waves as well. It promises wideband performance with almost unlimited bandwidth. Although described in literature more than 40 years ago such circuits did not find wide use. This article aims to demonstrate practical design and properties of a circuit based on log-periodic principle. The authors selected a balun consisting of a wideband equal power divider (Wilkinson type) and a 180-degree differential phase shifter. The shifter, based on log-periodic principle, consists of cells containing asymmetric striplines interconnected by offset broadside-coupled striplines. The resulting circuit covers two octaves centered at 1 GHz.