Advanced millimetre-wave antennas for future 5G communications

This research focuses on the design and development of millimetre-Wave (mmWave) antennas for future 5G communications. An exhaustive literature review was conducted to identify the challenges associated with emerging mmWave antennas. The thesis investigates a family of novel 5G antennas with unique characteristics including by their compact size, planar geometries, large area coverage, wide bandwidth, and single/multi-beam shaping capabilities.To address adjacent channel interference and spatial path fading losses in mmWave communications, a dual-band dual-beam antenna utilising double circular rings is proposed and developed (Chapter 3). This is the first antenna to generate dual beams in dual mmWave bands, offering a peak gain of 9.2 dBi and more than 20\% fractional bandwidth in both the bands. Building on this work, a novel tilted-beam end-fire antenna design based on double half-circular rings is explored, achieving stable radiation patterns over a wide operating range, suitable for both microwave and mmWave base stations applications (See Chapter 4). While dual-beam and tilted-beam antennas provide wide bandwidth, their limited area coverage restricts their applicability for unmanned aerial vehicle and base stations communications. To address this, novel slotted bent corrugated substrate integrated waveguide antennas for linearly polarised conical-beam and circularly polarised conical-beam configurations were proposed (See Chapter 5). Both antennas exhibit wideband behaviour with stable gain performance across the entire operating frequency range. Additionally, their radiation patterns remain highly stable at 24ᵒ ± 1ᵒin the elevation plane with front-to-back ratio exceeding 20 dB.There were very limited worked carried out in the design of 360ᵒ azimuth pattern reconfigurable antenna for mmWave frequency bands. Addressing this gap, the thesis introduces a novel 360ᵒ azimuth-plane {pattern reconfiguration antenna (PRA)} for 5G New Radio (NR), frequency range 2 communications. A grooved substrate integrated waveguide (SIW) geometry is proposed to resolve impedance matching challenges in circular SIW antennas when the vias were opened to achieve pattern reconfiguration (See Chapter 6). A unique design technique utilising 2D high-impedance surface was introduced, significantly enhancing the antenna's bandwidth (23.5–27.5 GHz) and gain (11.2 dBi). This is the first circular SIW antenna capable of generating dual beams and steering them 360ᵒ in the azimuth plane.To simplify fabrication and enable high multi-beam shaping capabilities, a novel bent corrugated design was proposed as an alternative of vias in circular SIW antennas. Open-ended quarter-wavelength bent corrugations surrounding a circular patch effectively manipulate the electric field (See Chapter 7). Active PIN diodes were integrated into the bent corrugations, introducing a new method to control surface currents and steer the electric field in desired directions. This is the first antenna utilising only 12 active switches to independently steer more than two beams across the entire azimuth plane. It achieved a peak gain of 9.2 dBi in single-beam scanning mode with a 30ᵒ scanning step-size. A prototype of the bent corrugated SIW antenna was fabricated with soldered PIN diodes, and the impact of soldering on performance was thoroughly analysed. A novel solution based on a defected ground plane was proposed to mitigate the effects of soldering inductance.All the proposed antennas in this thesis were fabricated and tested using in-house facilities at Loughborough University. The measurement results closely align with simulations, demonstrating that the proposed antennas are well-suited for future 5G base stations, and vehicular communications.