Miniaturized 20 GHz CPW quadrature coupler using capacitive loading

This paper describes coplanar waveguide (CPW) quadrature couplers that utilize metal–insulator–metal (MIM) capacitors at each corner, eliminating the need for air bridges and significantly reducing the coupler footprint. A 20 GHz coupler on high‐resistivity silicon with branch lengths of 40° (660 μm) is presented—the area is 80% smaller than a conventional design. A measured insertion loss of ∼4.5±0.5 dB was achieved at 20 GHz.