A substrate integrated waveguide probe applicable to broadband complex permittivity measurements

A planar-type open-ended coaxial probe with substrate integrated waveguide structure has been developed for broadband permittivity measurement. The proposed probe consists of a microstrip line, a shielded stripline, and a coaxial aperture. The shielded stripline was formed by placing via-hole arrays along the stripline to form a substrate integrated waveguide. To access the bandwidth of the proposed probe, back-to-back transmission lines with various via spacings are characterized. Based on this data, substrate integrated waveguide probes are designed and fabricated to measure the complex permittivity of 0.9 % saline up to 30 GHz. A 5 mm-wide substrate integrated waveguide probe with 2 mm via spacing shows distortion-free permittivity measurement up to 30 GHz, which is more than twice the bandwidth available from the conventional planar coaxial probe with the same probe width. The concept can be applied to silicon substrate, allowing a fully integrated active probe for broadband measurements.