On the Design of Fly's Eye Lenses at Sub-THz Frequencies for Wideband Communications

The expanding demand for high-speed wireless communications is pushing current networks and systems close to their limits. The use of sub-THz bands, where large bandwidth is available, is pointed out as one of the key strategies to cope with the huge amount of data transfer in the next Beyond 5G and 6G communications generations. Despite the promising properties of these high frequency bands, many challenges arise with their exploitation. The increasing loss due to propagation spreading, as well as the higher atmospheric and rain loss, should be compensated with highly directive antenna concepts. Besides, the lower output power provided by the transceivers in this spectrum and the increasing noise figure of the receiving devices magnifies the importance of achieving highly efficient antennas and transitions to the active front-end. The implementation of multi-beam architectures becomes specially challenging when moving to higher frequencies. The chip area does not decrease with frequency as passive RF structures do, due to the decreasing electronics efficiency, hindering the integration of the active circuitry together with the antennas. The harnessing of the large bandwidths available should be supported by all system and network layers, which will require breakthroughs in the related fields. This dissertation focuses in the development of wideband, efficient antenna concepts with multi-beam capability for the next communication generations. The use of elliptical lens antennas with resonant leaky-wave feeders is proposed, reaching aperture efficiencies higher than 70% over more than 35% bandwidth, for the first time with leaky-waves. Fly's eye lens architectures are introduced to cover small cell or point-to-multipoint use cases, where multiple, static beams are required. In order to evaluate the feeder and lens performance, an analysis in reception combined with spectral Green's functions is applied, enabling the optimization of lenses with diameters of  20. Making use of this methodology, four lens designs have been developed, fabricated, and characterized at G-band (140 - 220 GHz) and H-band (220 - 320 GHz). The lens concepts presented concentrate on some of the main requirements to be integrated in the envisioned Fly's eye 178 Summary arrays: wide bandwidth, high aperture efficiency, low loss (antenna and transition to frontend), circular polarization, large scan range. New measurement strategies are presented, applicable to the characterization of lens antennas in the sub-THz bands…