An Investigation of Parallel Plate Waveguide Terahertz Radiation Input Coupling

Quasi-optical and antenna-like ways of coupling free-space THz radiation into parallel-plate waveguide are examined. Cylindrical lenses made of cheap, off-the-shelf HDPE rods with 6, 10 and 16 mm diameter are used. A tapered input is also examined and it is found that in absolute terms the 16mm lens couples most radiation, but once the differences in effective aperture are accounted for, the tapered input is the best. 16mm and 6mm lenses proved to be sensitive to alignment and not very practical. FDTD simulations of the complete experimental setup are performed and show good qualitative agreement, especially inside the single-mode propagation region.