High/low-impedance transmission-line and coupledline filter networks for differential phase shifters

Two compact and simple to design differential phase shifter topologies, based on high/low-impedance transmission-line sections and open-ended coupled-line sections, are presented for the first time. The basic circuit theory for single section topologies is reviewed, leading to design equations and graphs for direct circuit synthesis. Balanced topologies and multiple section designs are also proposed improving the performance and feasibility of the phase shifters. Two planar microstrip single section differential phase shifter hybrids, at a centre frequency of 12 GHz and a 45 and 135 phase difference have been designed and manufactured. The designs have a simulated 0.5 dB amplitude and 1 phase imbalance over more than 25 and 40 bandwidth, respectively. Experimental results verify the circuit performance and feasibility of the proposed differential phase shifters.