Experimental verification of coplanar-to-substrate-integrated-waveguide interconnect on low-permittivity substrate

An interconnect between coplanar waveguide (CPW) and substrate integrated waveguide (SIW) is designed and experimentally verified. Common to regular SIW circuits is a low-permittivity substrate, whereas design formulas CPW usually assume a high permittivity. Therefore, commercially available field solvers are used in a parametric study to optimize the interconnect over a wide bandwidth between 18 GHz and 28 GHz. Cross-sectional field plots demonstrate its basic operation. The individual interconnect achieves return and insertion losses better than 20 dB and 0.5 dB, respectively, over the entire frequency range. The respective values for a measured back-to-back transition are 17 dB and 1.45 dB which are in good agreement with simulations.