Propagation of Single-Mode and Multi-Mode Terahertz Radiation Through a Parallel-Plate Waveguide

We investigated the propagation of singleand multi-mode terahertz (THz) radiation through a parallel-plate waveguide for various gap sizes of the plates and polarizations of the incoming THz eld. Single TEM (TM0) and TE1 modes within the 4-THz frequency range propagated through a waveguide with a plate separation of 103 m. Multi TE and TM modes were observed for a 360m separation. High-order modes have a very high group velocity dispersion near the cuto frequencies, which causes extensive pulse reshaping and broadening, in addition to multimode interference in the time and frequency region. The majority dominant mode is a combination of the TE1 (97.96 %) and the TM0 (81.61 %) modes because the lowest mode has a small absorption and an incident even eld pattern. Because each mode has di erent transmission and coupling coe cients, absorption and propagation constant, the theoretical calculation for the total TM or TE modes requires a summation of the components. The theoretical calculation and the measured data t well in the frequency and time domain.