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…@en

In this contribution, a broadband G-band leaky-wave (LW) fed lens antenna with an integrated dielectric grid polarizer is presented. The proposed wideband polarizer unit cell geometry enables its fabrication at frequencies higher than 100 GHz, presenting high transmission properties and low axial ratio (AR). A quasi-Analytic technique based on multilayer spectral Green's function combined with a numerical Floquet modes' solver is used to optimize the lens aperture efficiency and AR. The proposed technique is validated via full-wave (FW) simulations. A design is proposed in low dielectric permittivity material, achieving FW simulated aperture efficiency higher than 75% over 44% relative bandwidth, and an AR lower than 3 dB over 35% relative bandwidth. The antenna is able to achieve multiple directive circularly polarized (CP) beams when fed by a focal plane array, preserving the AR bandwidth. A prototype has been fabricated and measured, exhibiting an excellent agreement with quasi-Analytic and FW simulations.

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Thanks to the large bandwidth availability, millimeter and sub-millimeter wave systems are getting more attractive to be used in a wide range of applications, such as high-resolution radar or high-speed communications. In this contribution, a new lens antenna in-package solution is presented for the H-band (220320 GHz), including a wideband quartz-cavity leaky-wave feed combined with an air-bridge chip interconnect technology, based on spray coating and laser lithography. This interconnection acts as a wideband, low-loss transition between the GaAs front-end and the quartz antenna, avoiding the use of expensive waveguide split-blocks. An antenna prototype including the interconnect has been manufactured and characterized, validating the full-wave simulated results for the integrated H-band leaky-wave with aperture efficiency higher than 74% over 34% bandwidth, and radiation efficiency higher than 70% over 37% of bandwidth.

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Low relative permittivity plastic elliptical lenses in combination with integrated focal plane arrays are a promising solution to be used in the future mm- and sub-mm-wave systems. Their appeal lies in the availability of materials with moderate loss and lightweight, and the possibility to use cost-effective manufacturing techniques. However, the achievable scanning angular range is relatively small with low permittivity lenses. In this article, we explore the use of dielectric gratings with modulated height integrated in the lens material, with the aim of enlarging the steering angle. The dielectric gratings synthesize a tilted feed pattern, reducing the reflection loss and spillover when illuminating the lens off-focus. A quasi-analytic approach based on the Floquet mode analysis of the gratings is used to synthesize the grating profile. This method is combined with an analysis in reception of the lens antenna. A wideband prototype in $G$ -band (140-220 GHz) has been fabricated, achieving a field of view of ±25° with gain >30 dBi.

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In order to fulfill the exponential increase in the demand of high-speed wireless links, future XG wireless networks will be developed at higher carrier signal frequencies, reaching the hundreds of gigahertz. In this contribution, a leaky-wave-fed HDPE lens antenna working at ${G}$ -band which can be useful for future XG communications is presented. The proposed lens design enables the generation of up to 40 beams, with gains higher than 30 dB. Analytical tools have been applied to optimize the lens aperture efficiency, validating the results via full-wave simulations. The reached aperture efficiency for the broadside beam is higher than 80% over a 44% relative bandwidth. The measurement results for a fabricated prototype show excellent agreement with the simulated performance.@en

A high-gain broadband leaky-wave fed lens antenna with an integrated dielectric gratings polarizer covering the whole G-band (140-220GHz) is presented. This work focuses on the polarizer gratings manufacturing and in particular on the selection of plastic materials and the fabrication process refinement. The polarizer geometry has been designed and optimized to be compatible with standard milling techniques. A quasi-analytical method based on an analysis of the lens antenna in reception is used to validate the in-lens polarizer performance. Several prototypes have been fabricated, finally obtaining an excellent match between measurements and quasi-analytical results.

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In this paper, a leaky-wave fed lens antenna working at G-band for future XG communications is presented. A lens with a diameter of 16λ₀is proposed in HDPE material with a feed matching better than-10dB over a 45% of relative bandwidth. Analytical tools have been applied to achieve an aperture efficiency higher than 80% in the entire frequency band. One prototype have been fabricated and measured and the results agree well with the generated from both analytical approach and full-wave simulations.

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The exponentially increasing demand for highspeed wireless links can be only efficiently satisfied with the development of future XG wireless communication networks, based on higher carrier signal frequencies, starting from 100 GHz. In this contribution, a circularly polarized G-band leaky-wave fed lens antenna with an integrated dielectric grid polarizer is presented, which can fulfill the challenging requirements for these future XG networks. A design is proposed in low dielectric permittivity material with a feed matching better than -10dB over a 44 % of relative bandwidth. The circularly polarized lens aperture efficiency is higher than 75% over a 35 % relative bandwidth, with an axial ratio lower than 3dB. Analytical tools have been applied to optimize the lens aperture efficiency, validating the results via full wave simulations. A lens prototype has been now fabricated and is currently being measured.

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