Design and Analysis of LTCC-Integrated Planar Microstrip-to-Waveguide Transition at 300 GHz

A 300-GHz planar microstrip-to-waveguide transition in low-temperature co-fired ceramic (LTCC) is numerically and experimentally analyzed. A via fence and air holes are used to form a three-dimensional transition structure and a vertical hollow waveguide inside the multilayer LTCC substrate. The transition consists of a coplanar-waveguide-fed slot radiator backed by a short-wall of the waveguide and an open-circuited microstrip resonator. On the basis of the dual operation mechanism, the design guideline for the complex 3D structure is described using full wave analysis. The overall design is experimentally verified by a back-to-back transition which exhibits insertion loss of 4 dB at 300 GHz and 36-GHz bandwidth with better than 10-dB return loss. To evaluate the loss of a single transition, we carried out a loss component analysis by evaluating different lengths of microstrip line and hollow waveguide. The estimated loss for a single transition is 1 dB at 300 GHz. The planar transition without a metal back-short significantly reduces the size of terahertz packages and eliminates the need for additional components for hermetic sealing. The compact transition is easy to integrate in a low-cost LTCC package with an MMIC chip.