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The feasibility of a novel near-field focusing technique based on Time-Modulated Arrays (TMAs) is studied. The formulation for a near-field transmission problem is developed, showing its interesting potential for multi-user focusing at different frequencies, advantageously exploiting the characteristic TMA side frequencies radiation. Although asking for specific patterns at a set of different radiation frequencies may degrade the overall system performance, it is shown that the required radiated field distributions may still be achieved with acceptable focusing performance. This fact makes TMAs an interesting alternative to other technologies due to their simpler implementation through digital devices, also allowing for an adaptive implementation as required for many real applications. Some illustrative examples are presented., This work was partially supported by the Spanish \emph{Ministerio de Ciencia e Innovacion} and the Spanish Research Agency (AEI) under the projects ARTEINE (TEC2017-86619-R) {and ENHANCE-5G (PID2020-114172RB-C21 / AEI / 10.13039/501100011033)}, and by the Gobierno del Principado de Asturias under project GRUPIN-IDI-2018-000191. This work was supported in part by the Italian Ministry of Education and Research (MIUR) in the framework of the CrossLab project (Departments of Excellence).

A dual-polarized transmitarray antenna is proposed to generate a multi-zone coverage at 28 GHz for 5G indoor communications. The transmitarray radiates a constant power density within its near-field region over a specific area generating different spots in dual-polarization. The different spots are produced by feeding the transmitarray with a cluster of horn antennas, which are spatially distributed to obtain beams in different directions. The performance of the coverage is improved with a Phase-Only Synthesis (POS) of the transmission coefficients. The transmitarray is designed with dielectric-only elements, which provides a low-cost solution. The prototype is measured in a planar acquisition range, showing a high agreement with simulations. The proposed transmitarray together with the spatial feed distribution provides a potential alternative to generate multi-zone coverages in millimeter frequencies., This work was supported in part by the Ministerio de Ciencia, Innovación y Universidades under Project TEC2017-86619-R (ARTEINE); an d Ministerio de Ciencia e Innovación and Agencia Española de Investigación within Project ENHANCE-5G (PID2020-114172RB-C21-2/AEI/10.13039/501100011033).

In this work, a reflectarray antenna is presented as a dual-polarized plane wave generator (PWG) in mm-wave frequencies. The reflectarray produces a uniform plane wave within its near field in a volume close to the aperture. A dual-polarized pencil beam reflectarray is used as starting point to carry out a phase-only synthesis (POS) to reach a dual-polarized uniform plane wave. The synthesis aims to overcome the amplitude limitation due to the incident field while preserving the phase flatness. The phase distribution obtained in the POS is used to carry out a design based on sets of orthogonal-coplanar dipoles. This unit cell provides independent control of each polarization using a single-layer topology. The design is manufactured, and the prototype is measured in a planar acquisition range facility. The prototype shows discrepancies with simulation and further analysis is carried out. After finding out the proper value of the dielectric constant, a new design is carried out. The second prototype shows a good agreement with simulations, obtaining that reflectarray antennas are a suitable and low-profile solution to produce uniform plane waves within the near field., This work was supported in part by Ministerio de Ciencia e Innovación and Agencia Española de Investigación within the project PID2020-114172RB-C21/AEI/10.13039/501100011033, and by Gobierno del Principado de Asturias within the project AYUD/2021/51706.

In this paper, it is proposed the use of ultra-thin reflectarrays in some emerging scenarios in the new mm-wave cellular networks such as 5G, Beyond-5G (B5G), and future 6G. To that purpose, two dual-linear polarization reflectarrays are developed to provide coverages in different scenarios at the mm-waves band. Working at 28 GHz, reflectarray designs adapt the radiated field to the coverage area specified in each scenario, through an ultra-thin surface composed of simple cells. To evaluate the antenna performance, two reflectarray prototypes identical in size are manufactured and tested achieving a good trade-off between the performance and the low-cost, low losses and, low-profile characteristics of the antenna. This work demonstrates the good performance of simple topology reflectarrays, being an interesting antenna candidate in the upcoming wireless networks.