Innovative 3D-Printed Designs for Millimeter-Wave Lenses and Meta-Lens Antennas

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Over time, wireless communication networks have gained increasing importance, both for personal use and industrial and organizational applications. In fact, internet users are no longer just individuals, as the number of objects connected to the internet, known as the "Internet of Things" (IoT), has grown over time. The continuous increase in the number of users and the volume of data transmitted and received has made the data transmission provided by wireless communication systems insufficient. Consequently, these systems have been updated over time, progressing from one generation to the next. Currently, the fifth generation of wireless communication is in the process of being implemented for its initial applications. The fact that the amount of data transferred for each user is increasing has led communication systems to move to higher frequencies, as these frequencies allow for a greater bandwidth to be transferred. However, this increase in frequency is accompanied by an inevitable rise in free-space propagation losses, which are countered by increasing the gain of the antennas used. This has resulted in a significant increase in the research on high-gain antennas. As time has passed, not only have communication systems evolved, but other disciplines have evolved in tandem. An example of this is 3D-printing, which allows for the creation of complex and customized objects at a low cost, democratizing manufacturing for both individuals and small companies. Meanwhile, materials engineering has enabled the creation of various materials for use in 3D-printing, including different types of polymers, ceramics, and even metals. These materials are characterized not only by their elasticity, mechanical strength, or thermal capacity but also by their electromagnetic properties. Initially, antennas were designed using 3D-printing as a manufacturing method, using materials that, although not designed for electromagnetic applications, could still be used for this purpose. However, they presented a fundamental problem: high losses. This triggered various companies to design materials specifically for electromagnetic applications, with a specific permittivity value and, most importantly, low losses, even at millimeter-wave frequencies. This allowed researchers to consider this manufacturing method as part of the possibilities. All of this together has led to a large number of antennas being proposed for 5G applications, with prototypes manufactured using 3D-printing. Among the diverse range of proposed antennas that require only plastic materials, we can find dielectric resonators, leaky-wave antennas, dielectric polarizers for antennas, and lens antennas. The latter have gained popularity as communication systems have shifted to higher frequencies because, at these frequencies, the overall size of the lens decreases, making them suitable candidates. One advantage they offer is the simplicity in the design of their feeding network, which becomes increasingly valuable as the frequency increases and the size of the components decreases. For this reason, the motivation for this thesis lies in the investigation of lens antenna proposals designed for high-frequency applications, with the aim of serving as candidates for new wireless technologies, including the current 5G, the upcoming 6G, or any other future technology that may use millimeter-wave frequencies. 3D-printing will be used as the main manufacturing method throughout this thesis, allowing for the production of antennas with complex shapes at a low cost and with low losses. The thesis can be divided into two parts: lens antennas and meta-lenses. In the first category, four topologies of antennas have been investigated, all of them dielectric and designed to be manufactured using 3D-printing. Among them, a new lens antenna stands out, with the ability to convert linear polarization to circular without adding any extra devices. The novelty of the other antennas shown here lies in their specific design for 3D-printing and high-frequency applications, pushing the limits of 3D-printing for successful prototyping. The second part of this thesis focuses on the study of metasurfaces for lens antenna applications, where two periodic structures have been investigated, one dielectric and one metallic, both embedded into a parallel plate structure. With the first analyzed unit cell, two meta-lens antennas have been designed, a Luneburg lens and a Mikaelian lens. The second analyzed periodic structure consists of a new metallic unit cell that stands out for its high level of isotropy, making it an excellent candidate for lens antenna design. This has motivated the design of a Mikaelian lens antenna to demonstrate its how to take advantage of the properties of this unit cell.
Mención Internacional en el título de doctor
Wave propagation, Wireless communication systems, High-gain antennas, Dielectric lens antennas, 3D-printing
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