3D characterization of air bridges and via holes in conductor-backed coplanar waveguides for MMIC applications

A 3-D finite-difference time-domain (FDTD) method is used to characterize an air bridge and two via holes which can be used in a conductor-backed coplanar waveguide (CPW) to suppress the coupled slotlinelike mode. The accuracy of the analysis is demonstrated through a comparison of theoretical results obtained using the FDTD method to experimental results for a via hole ground in a microstrip. It is shown that the via hole discontinuity in a conductor-backed CPW is associated with reflection losses lower than those for an air bridge discontinuity. In both cases the CPW keeps its advantage of easy adaptation to both series and shunt element connections.<>