Numerical modelling and design of wideband electromagnetic structures at radio frequencies: Applications in cosmology and digital communications

Change log
Cumner, John 

This thesis discusses the use of computational electromagnetic simulation technology to simulate various physical scenarios for analysis and design.

Digital communications continue to dominate modern communication, and require increasing bandwidth to transfer the volume of information in use in today's society. One method for allowing these expansions is to improve the transmission through currently existing infrastructure, through improved impedance matching. The use of the surface wave mode of transmission is also considered to help improve data throughput, with a focus on the impedance of the required launchers. Simulated measurements for these impedances are calculated, with reference to their physical origins.

Also examined within this thesis is the application of computational electromagnetics to the global 21 cm experiment REACH. This experiment aims to detect a signal five orders of magnitude below the foreground signal, and so requires highly accurate and precise understanding of the radiometer instrument. Both the design and analysis of aspects of the REACH dipole radiometer are considered throughout this thesis.

While simulation of physical scenarios is to some degree accurate, it is inevitable that uncertainties will arise from simplifications made in computational models. So in the context of a dipole antenna's directivity pattern, and corresponding antenna temperature, the use of a parameterized sum of basis functions is considered to remodel the directivity of a physically perturbed antenna. Through the use of physically based basis functions and per frequency fitting, a rebuild accuracy within 0.1% of directivity is shown.

The effect of likely physical deviations in a ground plane is considered in the case of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) dipole radiometer. The physical deviations considered include the presence of soil, multiple and single dips in the ground plane. These alterations often induce uncertainties above 1 K, a level which would obscure a global 21 cm signal detection. Also noted is the impact of the addition of serrations to the edge of a square ground plane, with the replacement of large wavelike chromatic fluctuations with smaller pockmark type deviations.

Finally, I describe the implementation of a quantified figure of merit based design method of radio frequency electromagnetic situations. This is used for the design of the REACH global 21 cm dipole radiometer. The figures of merit considered encompass the impedance of the antenna in addition to the chromaticity of its directivity pattern and are combined in such a way as to allow even comparison between these important aspects of the antenna.

De Lera Acedo, Eloy
21 cm Cosmology, Antennas, Astrophysics, Computational Electromagnetics, Radiometer
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge
EPSRC (2137006)
Engineering and Physical Sciences Research Council (2137006)