A K-Band Wideband Air-Filled Coaxial Transmission Line With CNC-Machined Gap Waveguide Package

This paper reports on a new class of packaging scheme for air-filled self-suspended coaxial transmission lines (TLs) using gap waveguide technology. This scheme exploits a periodic electromagnetic bandgap (EBG) architecture of the gap waveguide and the EBG structure behaves as an alternative for the outer conductor of the coaxial TL. The coaxial TL packaged with the gap waveguide is capable of realizing single TEM-mode transmission in a wide bandwidth, without wave leakage from air gaps of the gap waveguide due to the attractive EBG characteristic. A gap-waveguide-packaged 50-O air-filled square coaxial TL operating at K band is designed and implemented. The TL is made out of copper by employing computer numerical controlled machining process. The manufactured TL demonstrates at 16-28 GHz an insertion loss (IL) of 0.36-1.09 dB (an estimated attenuation factor of lower than 0.35 dB/cm excluding the IL from RF connectors) and a group delay of 0.1-0.19 ns. The work indicates extensive applicability of the gap waveguide in the packaging of other air-filled coaxial TL-based passive components.