Improvement of THz coupling using a tapered parallel-plate waveguide.

This paper reports an experimental and simulation study of a tapered parallel-plate waveguide (TPPWG) to improve THz coupling to the plate separation gap. The flat- and round-type TPPWG without any silicon lens is compared to the parallel-plate waveguide (PPWG) with a plano-cylindrical silicon lens. The spectrum amplitudes of the input-side TPPWG and the input- and output-side TPPWG both having a 3 degrees slop angle increased about 56% and 103% at 1 THz when compared to that of the PPWG. Since the input- and output-side TPPWG had almost no impedance mismatch to the propagating THz wave, coupling to the waveguide could be improved twice compared with the PPWG.