A Coaxial to Air-Filled Substrate Integrated Waveguide Transition With Near-Octave Bandwidth

In this letter, a wideband coaxial to air-filled waveguide transition is proposed, which has been realized by the substrate integrated waveguide (SIW) technology. The present design incorporates several air-filled vias of varying hole diameter to efficiently match the impedance over a wide operating bandwidth in the dominant TE10 mode, hence replacing the need for dielectric taper or larger footprint. A transition prototype has been designed and tested to validate the results. The measured return lass is better than 15 dB and insertion loss of 1 +/- 0.1 dB over the band of interest (9.5-15 CHz), hence portraying a near-octave bandwidth from the proposed design.