Design and Measurements of Millimetre-Wave MIMO Antennas

In response to the growing demand for connectivity among end users, the fifth generation (5G) of communication systems emerged as a promising solution, employing Multiple-Input Multiple-Output (MIMO) technology for maximizing and shielding the generation resources for the same purpose. As a fundamental part of the technology, the design of wireless channels, for this case, has been evolving each time on the improving element of its performance resulting, at the same time, in complex and expensive RF prototypes. Specifically for an end user Multi-user MIMO (MU-MIMO) environment.
This thesis contributes to the design and understanding of open loop antenna arrays and
rectangular dielectric resonator antennas (RDRA) as main elements for MIMO with common Ground Plane (GP) scenarios as different design approaches for achieving high gain, wide bandwidth, and high radiation efficiencies with the simplest design methodology.
A comprehensive iterative open loop antenna array and RDRA design methodology started demonstrated, encompassing the design of 1, 2, and 4 antenna elements and examining the impact of their positioning on the MIMO system performance carried at the C-band and mmWave frequencies as part of the 5G/5GNR technology. An open loop antenna array at the mmWave with high gain and circular polarisation was initially considered, followed by an RDRA at the C-band with a similar design target as the initial case. mmWave designs were considered with linear and circular polarisation. Furthermore, mutual coupling simple reduction techniques were applied to the 4 antenna element systems to determine the most adequate to preserve the single antenna capabilities for the MIMO system and maintain at the same time an inter-element power reflection lower than -20 dB. The single and four RDRA element designs were fabricated and measured. The open loop antenna array demonstrated a gain of ∼14dBi sacrificing complexity and enhancing the coupling between MIMO elements. The proposed RDRA designs achieve simplicity and a potential antenna system overall size reduction showing at the same time a maximum gain of ∼7 dBi with a 4 splitted beams radiation pattern.