This paper an experimental study of a tapered parallel-plate waveguide(TPPWG) to improve THz coupling to the plate separation gap. Propagating THz waves has a small absorptance and no group velocity dispersion in PPWG 100um gap. However about 30% reflection loss from si lens and has loss to the structure problem. This loss induces a low coupling efficient.
To prevent the reflection loss and to concentrate the THz beam on the air gap, of the plate separation the structure of the input side of the PPWG was changed a tapered structure. The five different slop angles of the tapered part-i.e., 20˚,15˚,10˚,5˚, and 3˚ were used to get the THz pulses. As the slop angle of the TPPWG decreased, the amplitudes of the THz pulses were enhanced. Had the slop angle been smaller than 3˚, the measured THz pulse would have been enhanced more.
When the input THz beam was incidence to one-sided TPPWG has a reflection on boundary surface. To reduce the reflection, boundary surface made a changing round. When Compare The round TPPWG with non round TPPWG, increased by 15% at the peak to peak and was enhanced by 13% at the 1THz frequency.
And, the input-, output- side of the PPWG was changed a two-sided tapered structure. The peak to peak THz amplitude of the two-sided TPPWG improved by 138% compare with the PPWG. also improved by 38% compare with the one-sided TPPWG. The PPWG attenuation loss is considered, the two-sided TPPWG, the on-sided TPPWG and the PPWG had a respectively 56%, 42%, and 27% coupling.
Also, Use the PPWG and TPPWG, coupling improvement of TSP was generated on aluminum sheet. The improvement of TSP coupling the aluminum surface was done by the vertical-, horizontal-, and check grooves on the aluminum sheet with 50um thickness. The vertical and check grooves on the metal surface was 100% improved coupling efficient than that of the horizontal and smooth surfaces. Also, 0.5mm groove period had 100% improved coupling efficient compare with the 1.0mm groove period.
Although the amplitude of spectra to the vertical and check grooves was improved, the spectrum bandwidth was reduced compare with the horizontal and smooth surface.