Felipe Vico

Hands-on activities involving real instrumentation are known to increase student engagement and deepen conceptual understanding in engineering education. This paper reports a low-cost, portable outdoor experiment on antenna polarization designed and implemented by senior undergraduate students for first-year learners during a science outreach fair at the Universitat Politècnica de València. The setup employed a compact vector network analyzer and two circularly polarized antennas (helix and skew planar wheel) to demonstrate polarization alignment and rotation effects in real time. Qualitative observations and short structured prompts revealed increases in students’ ability to identify polarization types and relate them to measured responses. Technical issues—particularly VNA miscalibration—provided additional learning opportunities and informed improvements for future iterations. The results suggest that short, authentic demonstrations can effectively reinforce core concepts in electromagnetics and support peer-led learning environments.

Massive Multiple-Input Multiple-Output (MIMO) systems with hundreds or thousands of antenna elements are fundamental to next-generation wireless networks, promising unprecedented spectral efficiency through spatial multiplexing and beamforming. However, the computational burden of channel state information (CSI) acquisition and processing scales dramatically with array size, creating a critical bottleneck for practical deployments. While previous works demonstrated that Fast Fourier Transform (FFT)-based beamspace processing can exploit the inherent angular sparsity of wireless channels to compress CSI feedback, the digital implementation requires intensive computations that become prohibitive for ultra-large arrays. This paper presents an analog alternative using Butler matrices—passive beamforming networks that realize the Discrete Fourier Transform in hardware—combined with RF switching circuits to select only dominant angular components. We provide a comprehensive analysis of Butler matrix architectures for arrays up to 32 × 32 elements, characterizing insertion losses across different technologies (microstrip, substrate-integrated waveguide, and waveguide) and operating frequencies (10–30 GHz). The proposed system incorporates parallel power sensing with Winner-Take-All circuits for sub-microsecond beam selection, drastically reducing the number of active RF chains. Full-wave simulations and capacity evaluations at 12 and 30 GHz demonstrate that the Butler-based approach achieves comparable performance to FFT methods while offering significant advantages in power consumption and processing latency. For a 256 × 256 array, FFT computation requires 0.36 ms compared to near-instantaneous analog processing, making Butler matrices particularly attractive for real-time massive MIMO systems. These findings establish Butler matrix front-ends as a practical pathway toward scalable, energy-efficient beamspace processing in 6G networks.

Many integral equation-based methods are available for problems of time-harmonic electromagnetic scattering from perfect electric conductors. Among the many challenges that arise in such calculations are the avoidance of spurious resonances, robustness of the method to scatterers of non-trivial topology or multiscale features, stability under mesh refinement, ease of implementation with high-order basis functions, and behavior in the static limit. Since three-dimensional scattering is a challenging, large-scale problem, many of these issues have been historically difficult to investigate. It is only with the advent of fast algorithms for matrix-vector multiplies coupled with modern iterative methods that a careful study of these issues can be carried out effectively. Our focus here is on comparing the behavior of several integral equation formulations with regard to the issues noted above, namely: the well-known, standard electric, magnetic, and combined field integral equations with standard RWG basis functions, and the more modern non-resonant charge-current and decoupled potential integral equation. Numerical results are provided to demonstrate the behavior of each of these schemes. Furthermore, we provide some analytical properties and comparisons with the electric charge-current integral equation and the augmented regularized combined source integral equation.

Massive MIMO has emerged as a key enabler in modern wireless communication, delivering unparalleled spectral efficiency and connectivity. Yet, as antenna arrays become larger, significant obstacles arise in handling channel state information (CSI) feedback and the computational burden. This paper proposes a groundbreaking angular-domain transmission method that transitions from the conventional time–frequency domain to the angular domain. By employing projection-based transforms, akin to the FFT-based OFDMA model that introduced frequency-domain transmission with subcarriers, this technique exploits the inherent sparsity of massive MIMO channels in the angular domain, enabling data flows to be seamlessly mapped onto physical paths or rays. The resulting sparsity reduces signaling overhead and streamlines system complexity, making massive MIMO viable for next-generation networks. Simulation and empirical studies highlight how angular-domain strategies reduce feedback requirements, support Tera-bps data rates, and facilitate scalable designs for ultra-large-scale MIMO.

Este estudio analiza la implementación de una estrategia de innovación educativa en la asignatura Campos y Ondas del Grado en Ingeniería Físicaen la Universitat Politècnica de València (UPV). Mediante la integración de metodologías activas y herramientas digitales, se ha buscado potenciar la comprensión de los principios fundamentales del electromagnetismo y mejorar la experiencia de aprendizaje del alumnado. A partir del análisis de evidencias tangibles y encuestas realizadas a los estudiantes, se han identificado tendencias que sugieren un impacto positivo en la motivación, la participación en clase y la percepción de utilidad de los contenidos impartidos. Los resultados preliminares refuerzan la relevancia de este enfoque metodológico y plantean la necesidad de continuar con la evaluación de su efectividad a lo largo del curso.

This paper presents three realizations of a complete set with a horn antenna and a focusing Gradient Index (GRIN) lens in X-band. The set was specifically designed for advancing additive manufacturing (AM) of polymers with different materials and techniques. The set has three constituent parts: a horn antenna, a support, and a lens. The horn antenna is the active element and must be electrically conductive; it was manufactured with Rigid10K acrylic resin and subsequently metallized using an electroless process. The support needed to be light, robust, and electrically transparent, so that Polyamide 11 (PA11) was used. The lens realization was intended for a dielectric material whose permittivity varies with its density. Therefore, the dielectric permittivity and loss tangent of different polymeric materials used in AM at 2.45, 6.25, and 24.5 GHz were measured. In addition, stochastic and gyroid mesh structures have been studied. These structures allow for printing a volume that presents porosity, enabling control over material density. Measuring the dielectric characteristics of each material with each density enables the establishment of graphs that relate them. The sets were then manufactured, and their frequency response and radiation diagram were measured, showing excellent results when compared with the literature.

This paper presents three realizations of a whole set of horn antenna and focusing Gradient Index (GRIN) lens in X band. The set was specifically designed for getting advance of additive manufacturing (AM) of polymers with different materials and techniques. The set has three constructive parts: a horn antenna, a support and a lens. The horn antenna is the active element and must be electrically conductive, it was manufactured with Rigid10K acrylic resin and subsequently metallised using an electroless process. The support needed to be light, robust and electrically transparent, so that Polyamide 11 (PA11) was used. The lens realization intended a dielectric material whose permittivity varies with its density. So that, we measured both dielectric permittivity and loss tangent of different polymeric materials used in AM at 2.45, 6.25 and 24.5 GHz. In addition, stochastic and gyroid mesh structures have been studied. These structures allow printing a volume that presents porosity, enabling control over the material density. Measuring the dielectric characteristics of each material with each density enables establishing graphs that relate them. The sets were then manufactured and their frequency response and radiation diagram were measured, showing excellent results when compared with literature.

In this study, we employ the adjoint method to design a Gradient Index (GRIN) lens at 10 GHz, optimizing the dielectric constant at each point to meet specific goal functions. Our optimization framework incorporates a 2D FFT-integral equation solver, delivering solutions within seconds. The entire optimization process is completed in just minutes, presenting a highly efficient approach to lens design. The optimized lens is fabricated using advanced 3D printing techniques, ensuring high precision and costeffective manufacturing. The resulting design features a unique ring-shaped lens with a central piece of lower contrast, weighing a total of 207 grams and achieving an aperture efficiency of 55.9 experimentally measured, confirming the effectiveness of the proposed method. The 3D printing process facilitates the rapid prototyping of such GRIN lenses, demonstrating its potential for applications requiring lightweight and compact designs. This approach opens avenues for further optimization and practical applications in communication systems and beyond.

In the rapidly evolving domain of wireless communications, the demand for higher data rates and improved channel capacities is ever-present. This paper introduces a novel approach to meeting these demands through Multimodal DirectRay Transmission (MDRT), a technique designed to enhance wireless channel capacity significantly. The essence of MDRT lies in a novel asymptotic expansion of the near field, leading to the formation of orthogonal channels with a power decay described by 1 r2n , n “ 1, 2, 3, . . . . Investigating both theoretical framework and practical implementations, this study not only elucidates the underlying principles of MDRT but also validates its feasibility through an experimental setup using two ad-hoc antennas. This empirical embodiment of the concept confirms its alignment with theoretical predictions and effectively demonstrates the technique’s practical viability. Located just below the far-field limit, the antennas operate in a regime where traditional interference and channel capacity models do not fully apply. By exploiting this underutilized spatial domain, MDRT substantially increases bitrate without necessitating additional spectrum or higher power consumption. This approach paves the way for more efficient use of the electromagnetic spectrum and offers a scalable solution to the bottleneck of point-to-point wireless channel capacity under certain conditions.