Novel uniplanar synthesized coplanar waveguide and the application to miniaturized rat-race coupler

By utilizing quasi-lumped components, we propose a novel slow-wave uniplanar synthesized coplanar waveguide (USCPW) in this paper. The physical length of a 90-degree uniplanar synthesized coplanar waveguide (USCPW) is less than one-twentieth of a guided wavelength. A lumped equivalent circuit model is proposed to explain the complicated behavior of the synthesized line. The design concept, propagation characteristics, equivalent circuit model, and simulated and measured results are carefully studied. Based on the new synthesized coplanar waveguide, a novel miniaturized rat-race coupler is demonstrated. The proposed design is merely 7.2% the size of a conventional coupler, which is the smallest one ever reported in coplanar waveguide form using printed circuit board technology. The response of the miniaturized coupler is experimentally verified in this paper.