Document Type

Theses, Ph.D

Rights

This item is available under a Creative Commons License for non-commercial use only

Abstract

The thesis describes a study of antennas for solutions in emerging systems. An account of the fundamental principles of these antennas is given together with an outline of the basic electromagnetic theory on which the designs are based. While the main focus is on antennas for Ultra Wideband (UWB) systems, some additional work was carried out on enhancing performance of circularly polarised antennas for satellite navigation systems. The study focussed on the design of highly efficient broadband antennas with particular requirements for size compactness, gain stability, phase-linearity, and the use of low-cost materials. These requirements are particularly important for UWB system antennas that operate in the Federal Communications Commission (FCC) allocated frequency range 3.1-10.6GHz. Very compact solutions were produced in the form of small semi-planar monopole antennas with broad bandwidth impedance and stable radiation properties that showed independence from groundplane dimensions. The investigation of the broadband properties of a rolled planar monopole led to a unique mechanically-reconfigurable antenna, operating in the UWB spectrum, for indoor or mobile applications where tuneable band-notching and omni-directional radiation are required. The impedance matching of this rolled monopole antenna can be adjusted by regulation of the degree of spiral tightness. This innovative solution overcomes several problems which are typical for traditional reconfigurable antennas, such as non-linearity, low gain/efficiency and limited power handling. The requirement for pulse-based UWB communication antennas that exhibit linear-phase led to the investigation of the frequency and time-domain performances of tapered feedlines for non-planar monopoles. By configuring an optimised taper between an antenna’s feed-point and radiating structure, the phase distortions can be significantly reduced without degrading the radiation characteristics. This principle has been proven to be successful for both two and three dimensional monopole antennas. Electromagnetic bandgap (EBG) solutions were proposed for proposing circularly polarised (CP) antennas for Global Positioning Systems (GPS) applications. Miniaturized EBG solutions based on fractal geometries were designed and integrated with stacked CP patch antennas. A radical EBG cell distribution around a CP patch antenna was also proposed. Compared to legacy Cartesian configuration designs, the radical EBG arrangement enhances the axial-ratio performance, reduces the antenna area footprint and simplifies the design of the guard ring between radiator and EBG cells.

DOI

10.21427/D7DG7D