Modelling of Electromagnetic Surface Wave Propagation for High-Speed Communications

Surface waves have been known as a low-loss electromagnetic mode supported by a single conductor for well over a century but little research has been dedicated to surface wave interactions with its surroundings and surface wave propagation on printed circuit boards and on multiple wires. This thesis establishes novel analytic models, numerical simulations and experimental results in these areas and uses these insights to assess the application of surface waves with particular focus on telecommunications. To begin with, well-known surface wave solutions are reviewed. Radiation induced by dielectric material in the vicinity of the binding structure is discussed as a potential loss mechanism of propagating surface waves. In addition, a model is developed for the planar Goubau line consisting of a single conducting trace on a dielectric substrate. The model assumes lossless materials and replaces the conducting trace by a current filament. A boundary condition is imposed on the electromagnetic field to determine the phase constant of the supported surface wave. The results of the model are consistent with numerical solutions using the COMSOL software package and with experiments. Next, surface waves on uniform two-wire and multi-conductor systems are studied. Two-wire systems are modelled perturbatively by assuming that the two-wire modes are a superposition of single-wire surface waves. By neglecting all but the fundamental surface wave mode, approximate expressions for the propagation constant and loss are derived and solved. The results are compared to experimental and numerical analysis and show high consistency when the wire separation is much larger than their radius. The methodology is generalised to an arbitrary number of conductors but quickly increases in computational complexity. Hence, an alternative approach is developed where surface waves are represented by a transmission line segment. Per-unit-length transmission line parameters are derived under the assumption that the coupled electromagnetic field is approximated by a superposition of fundamental surface waves on each wire. The system can then be treated as a coupled many-conductor transmission line system. Phase and attenuation constant of modes supported by the coupled system are compared to experimental results and to numerical simulations. Results agree well when the wire separation compared to the radius is large. The final part of the thesis investigates non-uniform systems supporting surface waves. In particular, twisted pair cables are studied. Experimentally observed stop bands are explained through contradirectional mode coupling which can occur in systems without helical symmetry. The many-conductor transmission line model for surface waves on uniform systems is adapted to simulate the non-uniform twisted pair cables. The stop band of systems containing a single twisted pair together with one or two straight wires are analysed experimentally, numerically and with the transmission line model. Further investigations into systems containing multiple twisted pairs with different twist rates show stop bands associated with the twist rate of each pair. Stop bands are predicted by the transmission line model but the simulated shape and frequency are only approximate because all systems considered have closely bundled conductors. The simulation tool CST Microwave Studio shows better accuracy in predicting the stop bands. However, code runtime for simulations are much greater than for the transmission line model developed in this thesis. The results of this thesis play an import part in assessing the applicability of surface waves as a high-speed communications channel. The research into surface waves supported by two or more conductors including the analysis of twisted pair cables is especially valuable because these are common cables found in the deployed telecom infrastructure. When stop bands are avoided on these cables, surface waves can be used to transmit broadband data signals over large distances subject to deployment scenarios.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Schaich, Tobias

Advisor dc:contributor.advisor

• Payne, Mike

• Electromagnetism
• Surface Waves
• Goubau Line
• Maxwell's Equations

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0001-9636-4308

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/342293