Microwave 3-dB four-conductor quadrature coupler based on asymmetrical CPW coupled lines

In the paper, a 3-dB quadrature coupler is developed by interdigitated asymmetrical four-conductor CPWs, while its feeding structures are implemented by four microstrip lines. In order to accurately extract the c- and π-mode impedances of the four-conductor asymmetrical coupled lines, a simulator-aided design method is proposed in this paper to overcome the simulation limitation of the commercial electromagnetic simulator. The experimental results not only demonstrate the effectiveness of the developed design procedures, but also reveal that the developed coupler has properties of wideband and flat quadrature phase differences between output ports.