Study of Design Principles and Optimisation Techniques for Ultra-Wideband Printed Antennas

TitleStudy of Design Principles and Optimisation Techniques for Ultra-Wideband Printed Antennas
Publication TypeThesis
Year of Publication2008
AuthorsJohn, M
Academic DepartmentSchool of Electronic and Communications Engineering
Pagination149
UniversityDublin Institute of Technology
CityDublin, Ireland
Thesis TypePhD Thesis
Abstract

This thesis deals with the design, optimisation and analysis of printed monopole antennas. Preliminary investigation focuses on printed strip, multibranch and rectangular patch monopole antennas. Furthermore, the effects of offset feeding and modifications to the groundplane are studied.

The main part of the thesis introduces novel geometries and optimisation techniques. A genetic algorithm (GA) is introduced and is applied to ultra-wideband (UWB) antenna optimisation problems. This algorithm is based on the concept of natural evolution. It mimics biological processes such as selection, crossover and mutation to evolve a set of trial solutions towards an optimum. A variety of geometries are developed to which the GA is applied. Optimisation goals focus on widening the impedance bandwidth, reduction of the lower edge frequency, improving linearity of the phase response, minimising variations in group delay and miniaturisation.

A novel geometry is developed which is based on quadratic Bezier spline curves. This allows limiting the number of parameters used to control the geometry. Thereby reducing complexity in the GA optimisation and thus, speeding up the design process. This technique is used for the radiating element as well as the groundplane of printed UWB monopoles.

A more efficient global optimisation (EGO) method is adopted to electromagnetic problems. This algorithm is designed to solve multi-objective optimisation problems where each function evaluation is temporally or otherwise expensive. With the time taken by an EM solver being typically in the order of minutes, electromagnetic problems are ideal candidates for this optimisation algorithm. The algorithm is suited for scenarios where computational power is limited or only a single license for commercial electromagnetic code is available, and thus, parallelisation is not an option. This method is used to optimise a variety of spline based UWB monopole antennas.

Resulting optimised antenna geometries from the GA and EGO algorithms are prototyped. The performance of these prototypes is thoroughly evaluated in an anechoic chamber. It is shown that the design principles and optimisation techniques developed in this thesis are suitable to generate antennas meeting a variety of requirements such as impedance bandwidth, gain, radiation pattern stability, efficiency, size and other design constraints.

Finally, an integrated module comprising three antennas is built to be fitted into a planned Dell Inspiron laptop. In a confined space a combined Bluetooth/UWB antenna and two WLAN antennas are realised, meeting strict performance standards and design constraints.

Funder

CTVR - The Telecommunications Research Centre,
Science Foundation Ireland

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