Compact Microstrip to Empty Substrate-Integrated Coaxial Line Transition

Substrate-integrated waveguides (SIWs) are increasingly being used due to their capability of combining the advantages of planar circuits and traditional waveguides. The development of empty SIWs has substantially reduced the related insertion losses, since waves propagate through air instead of propagating through a lossy dielectric medium. Recently, a new empty coaxial structure, completely built with printed circuit boards and integrated in a substrate, has been proposed. It has been named empty substrate-integrated coaxial line (ESICL). The resulting coaxial line has low cost, easy manufacturing, low radiation, low losses, high-quality factor, and nondispersive. A transition from grounded coplanar waveguide to ESICL already exists. In this letter, a transition from microstrip to ESICL is presented for the first time. In order to demonstrate its feasibility, a back-to-back structure and a bandpass filter have been manufactured and measured.