Miniaturized Coupled-Line Couplers Using Uniplanar Synthesized Coplanar Waveguides

A novel slow-wave synthesized coplanar waveguide (CPW), namely, the uniplanar synthesized CPW, is investigated in this paper. Quasi-lumped CPW inductors and capacitors are used in synthesizing the new slow-wave structure. The synthesis method, lumped equivalent-circuit model, and simulated and experimental results are discussed. The synthesized line, featuring excellent miniaturization capabilities, has a moderate quality factor. The slow wave factor is 7.5, while the unloaded quality factor is 30-60. By utilizing the synthesized CPW, three novel miniaturized coupled-line directional couplers are proposed and experimentally verified. With the help of even/odd-mode analysis, design charts are summarized for understanding of the developed miniaturized couplers. When compared with previous designs, the miniaturized couplers show comparable performance, but significantly reduced sizes. Additionally, they have quasi-square appearances, which are suitable for circuit integration in cascade connection.