HE11 Mode Based Wireless Communication for a Hyperloop System Using a Dielectric Lined Waveguide

Abstract

This study investigates a waveguide-based communication method for Hyperloop systems by analyzing the electromagnetic propagation characteristics inside a large, low-pressure metallic tube. The Hyper- loop tube, typically 3.3 m in diameter, behaves as an oversized circular waveguide in which multiple higher-order modes propagate simultaneously in the 3.5 GHz band, leading to modal interference, dis- persion, and phase instability. To overcome these limitations, this work focuses on the selective excita- tion and stable propagation of the low-loss hybrid HE11 mode. Two candidate transmission structures are considered: a corrugated waveguide and a dielectric- lined waveguide (DLWG). While the corrugated waveguide supports the HE11 mode through precisely machined quarter-wavelength corrugations, the DLWG achieves similar behavior by controlling the di- electric lining thickness on the metallic wall, offering structural simplicity and design flexibility. To experimentally validate these concepts, a 1/52 scaled model corresponding to a 63.5-mm, 182- GHz waveguide was designed. A Gaussian beam launcher, consisting of a corrugated horn antenna and a plano-convex lens, was implemented to excite the HE11 mode with high purity. The effects of beam offset and angular tilt were analyzed theoretically, numerically, and experimentally, confirming that angular tilt causes substantially greater modal degradation than lateral offset. A precision alignment stage was developed to minimize these errors during measurements. Field-pattern and S21 measurements of the scaled corrugated waveguide and DLWG were performed in the Fresnel region. Both structures exhibited stable HE11-mode propagation beyond the reactive near- field boundary, and the DLWG demonstrated HE11 characteristics comparable to those of the corrugated waveguide. Additional experiments involving an aluminum-coated scaled pod revealed significant dis- tortion of the HE11 mode, resulting in reduced transmission efficiency. The results further suggest that the DLWG structure designed for the 182-GHz scaled Hyperloop environment is also applicable to Electron Cyclotron Resonance Heating (ECRH) transmission systems in fusion devices. Since the DLWG forms the HE11-like mode through dielectric-thickness optimization rather than precision metallic machining, it provides a viable alternative transmission-line configuration for high-power millimeter-wave applications. Overall, this study demonstrates the feasibility of HE11-based communication inside the Hyperloop tube and highlights the potential of the DLWG as a simplified and scalable transmission-line solution for both Hyperloop channels and fusion ECRH systems.