A portable picocell antenna for 5G

Deployable emergency communication systems are a backbone solution for replacing damaged network infrastructures and/or providing high-end services in case of an emergency event. It is important that such systems are up-to-date with the latest mobile network technology, for enabling connectivity to users and profiting from its enhanced capabilities. The advent of 5G promises higher data rates, lower latencies and improved quality of services when compared to previous generations. To achieve that, mm-Waves have been identified as a key element due to the wide available spectrum. The implementation of deployable emergency communication systems compatible with 5G mm-Waves technologies, thus benefiting from its prospective advantages, is of great interest. This thesis focuses on 5G mm-Waves antenna design for this kind of applications. The high network capacity demand, the unfavourable channel conditions at mm-Waves and the still underdeveloped related radio frequency (RF) technology define a group of challenging requirements on the antenna design. While directive antennas are required to mitigate the attenuation with distance at these bands, omnidirectional coverage still needs to be provided. In addition, wide bandwidth operation, high efficiency, and low cost and power consumption are desired. In this context, antennas with multibeam forming capabilities have been widely acknowledged as a key enabling technology to support 5G wireless communications, representing an attractive solution to provide omnidirectional coverage while supporting Multiple Input Multiple Output (MIMO) techniques.

In this thesis, the design and implementation of a broadband efficient multibeam antenna for a portable picocell station are investigated. The picocell scenario in the context of emergency communications is studied and the antenna link budget is calculated considering mm-Waves propagation properties and available information on the upcoming standard. This leads to the definition of the design requirements and a preliminary antenna architecture that consists of an MxN antenna fed by a hybrid beamforming network (HBFN). This architecture is a promising approach for making multibeam antennas cost- and energy-efficient according to the latest research. The synthesis of the HBFN was realized considering the design constraints in elevation and azimuth such that the subarray, fed by an analog beamforming network, provides a csc2 pattern shape in elevation while M subarrays are controlled by a digital beamforming network to generate multiple orthogonal beams in azimuth. The antenna subarray was designed, fabricated and measured. Based on this, a study of the antenna array beamsteering capabilities in azimuth was carried out. After investigating the main parameters involved in improving its performance, the subarray design was optimized accordingly. The proposed antenna consists in a 12x6 array that works at 26 GHz with an impedance bandwidth higher than 12%. The radiation pattern shape in elevation is preserved over 7.3% of bandwidth. The antenna gain is superior to 10 dBi along the band of interest with a maximum value of 15 dBi. Simulated and measured results were compared, and the antenna beamsteering performance was tested for different sets of constraints indicating promising capabilities for a wide range of deployment scenarios. The proposed and validated design meets the requirements of the targeted applications on a practical low-profile implementation.