Suspended-strip gap waveguide coupled-line properties for Ka-band component design

Gap waveguides have been shown in the last years as a possible waveguiding solution in mm-wave band. These wave-guides do not require neither metal contact nor dielectrics. In particular, quasi-TEM transmission lines avoiding the high dielectric losses of materials at mm-wave frequencies can be designed with such structures. An interesting case is the Suspended-Strip Gap Waveguide (SSGW) which allows a fixed design of the pin lattice with possible re-utilization. Nevertheless, characterization of this transmission is still far from the well-known design expressions and charts available for classical transmission lines. This work addresses this problem, presenting an study of the impedance of the SSGW in the Ka-band which includes odd and even impedances of SSGW coupled lines. These data have been used to design a order-2 Chebyshev-type coupled-line filter, showing promising results.