Measurement and Modeling of Dielectric Tube Waveguidesfor Terahertz Pulses

摘要

The advent of terahertz (THz) spectroscopy and imaging has motivated the investigation of waveguides structures that axe appropriate for use at THz frequencies. Currently, most spectroscopy systems have no guiding mechimism and therefore suffer spherical spreading loss. The ideal waveguide would eliminate these spreading losses. have low attenuation and dispersion, and high field confinement. Effective terahertz spectroscopy also requires especially large bandwidths to identify spectral signatures; therefore single-mode propagation is necessary to transmit broadband pulses. Single-mode waveguides call be achieved by utilizing the fundamental HEM_(11) mode, which has no cutoff frequency, or by suppressing higher order modes. In this work, we present cylindrical, hollow-core, dielectric waveguides for the G-band (110-220 GHz). We will show propagation characteristics obtained by theoretical analysis, computer simulation, and experiments conducted using a vector network analyzer (VNA) with a cylindrical horn at tachment. The analytical model, in particular, will provide an additional capability to quickly predict waveguide behavior for a variety of applications. This complete model will predict both the number of supported and propagating modes and the means to source them. We will show that the number of supported modes depends primarily on the thickness and dielectric constant of the outer layer. 13y choosing proper dimensions and materials, single-mode waveguides call potentially be designed and realized to achieve all. of the aforementioned terahertz spectroscopy requirements.