Design and evaluation of diversity antennas and slot arrays

The increasing frequencies used in wireless communications now allow multi-element antennas (MEAs) to be physically small enough to fit on hand-held terminals. The role of the antenna is to transform between free-space waves and electronic signals, and its critical importance is that this transformation is the biting constraint for the performance of the entire wireless system. For example, two basic resources for wireless communications are
bandwidth and spatial support (size of the terminal), and the electrical size of the antenna fundamentally governs the tradeoff between these. Especially for mobile communications, the need for compact terminals and the demand for spectral and power efficiencies have been drivers of the adoption of MEAs for diversity and other multiple-input, multipleouput (MIMO) techniques. However, a methodology for the general design and evaluation for MEAs is not yet well established. This thesis addresses the evaluation of MEAs for diversity/MIMO, and also investigates single-port MEA designs comprising slotted waveguide arrays. The first part reviews techniques for antenna diversity/MIMO. It presents discussion and interpretation of the still-evolving diversity metrics, and benchmark antenna designs with new numerical and physical results for better understanding the evaluation processes. Pattern measurement is particularly challenging, but patterns are critical antenna parameters and are used in diversity performance metrics. The practical accuracy of pattern measurements is therefore included in the thesis. The second part looks into slot antennas for MEAs which strive to be compact, wideband, high efficiency and have low-cost integration with the terminal. Some applications call for antennas on, or within, an electrically small, curved metallic platform, such as a mast, or the struts of unmanned aerial vehicles, drones and bicycle frames. New designs of slotted coaxial waveguide antennas are presented which are more compact and have wider bandwidth than previously known designs.