{'fraction_non_alphanumeric': 0.02211595935445308, 'fraction_numerical': 0.004781829049611476, 'mean_word_length': 5.777327935222672, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Measurement and modeling of dielectric tube waveguides for terahertz pulses

The advent of terahertz (THz) spectroscopy and imaging has motivated the investigation of waveguides structures that are appropriate for use at THz frequencies. Currently, most spectroscopy systems have no guiding mechanism 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 can be achieved by utilizing the fundamental HEM11 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 (140-220 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 attachment. 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. By choosing proper dimensions and materials, single-mode waveguides can potentially be designed and realized to achieve all of the aforementioned terahertz spectroscopy requirements.