Geometry-Standardized CPW Dual-Coupling for Nominal 50 Ω Impedance Matching Across Multiple Micron-Scale Film Thicknesses

In this paper, a novel coplanar waveguide (CPW) structure featuring top-layer geometry invariant capabilities, loaded with a defected ground structure (DGS) that serves as a CPW impedance regulator, is presented. The proposed CPW transmission line (txline) keeps the 50 Ω impedance stable across micron-thick films of various thicknesses without requiring changes to the CPW dimensions. This CPW model obviates the need for repetitive CPW structure design over different film thicknesses for impedance tuning while simultaneously offering manufacturing standardisation. A critical limitation in conventional CPW and Grounded CPW (GCPW) is the significant dependence of impedance on substrate thickness, requiring re-optimisation of txline width (S) and slot gap width (Ws) for each substrate variation. Both conventional CPW and GCPW need concurrent modification ofSand Wsto reach 50 Ω impedance. In contrast, the proposed CPW model can match the 50 Ω impedance by tuning only a single parameter, the DGS width, Rsw(range between 3.08 mm - 3.16 mm). At a fixed CPW geometry, this model exhibits low characteristic impedance sensitivity to substrate variations, averaging 0.003 Ω/μm, which is 23 times lower than conventional CPW and GCPW (0.07 Ω/μm). When embedded into an antenna system, it has demonstrated an excellent S11 response, with simulation and measurement results showing a close match, with only a 1.44% frequency shift and a 2.98% S11 magnitude deviation.