Programa del congreso

This study numerically investigates frequency translation in a metasurface with spatiotemporal refractive index modulation using the Finite-Difference Time-Domain (FDTD) method. A TE-polarized monochromatic wave undergoes diffraction into spatial and temporal harmonics, dictated by the modulation parameters. Simulations illustrate frequency translation and analyze the effects of spatial period, modulating waveform, and metasurface thickness. The results align with the theory that classifies harmonics as evanescent or propagating and determines their diffraction angles.

Este trabajo explora y valida la aplicación del método de la matriz de transferencia multimodal (MMTMM) para el análisis preciso de estructuras unidireccionalmente periódicas radiantes de ondas de fuga. El método ofrece una metodología sistemática para calcular los números de onda complejos de los modos de fuga propios e impropios utilizando la matriz de transferencia multimodal de una única celda unidad, que puede obtenerse con software comercial. La versatilidad y precisión del MMTMM se validan con estructuras periódicas complejas que soportan ondas superficiales y que se utilizan habitualmente en antenas de fuga, incluyendo superficies corrugadas y tiras metálicas sobre dieléctricos. Los resultados se contrastan con soluciones obtenidas mediante el método de los momentos. La fiabilidad del método queda demostrada por la convergencia de las soluciones de múltiples simulaciones. El MMTMM demuestra ser eficiente, preciso y fiable para obtener la constante de atenuación y el desfase de estructuras abiertas 1D-periódicas.

This contribution presents a rigorous methodology for the design of parallel-plate leaky wave antennas (LWAs) based on bianisotropic Huygens' metasurfaces (BHMS). A slowly varying amplitude approximation (SVAA) is employed to overcome previous limitations in the leakage factor value, enabling a precise control of the aperture field distribution and, consequently, radiation pattern shaping capabilities. A field-based semi-analytical algorithm is used to synthesize the BHMS multi-layered unit cells, taking into account inter-layer near-field coupling effects without full-wave optimization. The potential and efficiency of this approach is validated through the fabrication and measurement of two prototypes with different characteristics, showing strong correlation between theoretical, simulated and experimental results.

This work presents the design, simulation, and experimental validation of a 1-bit Reconfigurable Intelligent Surface (RIS) based on slots controlled by PIN diodes, which modify the phase of the reflected wave. Unlike other solutions based on MEMS, varactors, and similar technologies, this approach offers a simpler and more scalable design, allowing expansion to higher-bit configurations without requiring major architectural changes.

The fabricated prototype demonstrates that this RIS can effectively control beamforming and signal direction. In contrast to traditional designs requiring visible biasing networks, the biasing network for the diodes is placed beneath the ground plane that contains the slots, which prevents electromagnetic interference and significantly simplifies integration. Simulations have been validated through experimental measurements, confirming efficient phase control.

This conference paper introduces a procedure for designing dual-band frequency selective surfaces (FSSs) with orthogonal linear polarizations. The FSS consists of a four-layered dielectric substrate with five metallization levels. The metallization levels alternate between periodic arrays of patches and periodic arrays of apertures. In the lower passband of the designed FSS only the polarization in the x direction is transmitted, while in the upper passband only the polarization in the y direction is transmitted. In a first step, the dimensions of the FSS are adjusted to obtain third order filtering responses. In a second step, a combined optimization in both bands is performed. The final design presents bandwidths of 20 % in the lower band (centered at 7 GHz) and 31 % in the upper band (centered at 12.6 GHz). It has a polarization isolation of 20 dB and its response is stable up to 30 degrees.

This paper presents the design, fabrication and experimental validation of a mechanically reconfigurable 2-bit unit cell for desigining reconfigurable intelligent surface (RIS). An optimized design has been developed, based on the controlled displacement of a metallized movable element driven by a stepper micromotor. This approach achieves a 90º ± 20º phase shift between states with losses below 1.09 dB in the n258 FR2 band of 5G (26 GHz). Additionally, a low-cost fabrication methodology has been carried out, using high-precision SLA 3-D printing and aerosol metallization. Finally, a RIS prototype was characterized in an anechoic chamber demonstrating good agreement between simulated and measured scattering patterns.

Se presenta el diseño de un polarizador dieléctrico conformado esféricamente e impreso en 3D para aplicaciones de comunicaciones en banda Ka. Está compuesto por láminas dieléctricas que siguen una trayectoria loxodrómica, lo que permite la conversión de la polarización lineal de una onda esférica incidente a polarización circular. Cuando el polarizador se ilumina con una antena omnidireccional de polarización lineal según la dirección polar, el polarizador permite radiar una onda esférica con polarización circular a izquierdas, mientras que, si la polarización de la antena es lineal según la dirección acimutal, la conversión de polarización se produce a polarización circular a derechas. Su comportamiento es evaluado con un diseño en el rango 37-40 GHz, en el que se utiliza una antena omnidireccional de doble polarización lineal para excitarlo. Tanto la antena como el polarizador se fabrican mediante técnicas de manufactura aditiva. Los resultados experimentales concuerdan en buena medida con las simulaciones.

Este trabajo presenta una antena monopulso a través de una bocina de fugas (LH) basada en la tecnología de guía de ondas integrada en sustrato (SIW). La LH consta de dos antenas de fuga (LWA) en tecnología SIW separadas angularmente para formar la apertura de la bocina. Diseñando adecuadamente esta separación angular junto a la dirección de radiación de las LWAs, se consigue un frente de onda plano. Para el comportamiento monopulso, se incluye un acoplador híbrido y desfasadores. Dependiendo del puerto de entrada, las LWAs se alimentan en fase o en contrafase generando los patrones suma y diferencia. Se ha fabricado un prototipo para validar el diseño. La bocina presenta una diferencia entre el diagrama de suma y diferencia en el eje de apuntamiento de -25.8 dB, una ganancia máxima de 12.9 dBi, y un ancho de haz de 6.4º a 27.5 GHz.

Este trabajo presenta el diseño y la validación experimental de un filtro de cavidad de guía de onda en banda W que opera en torno a 91\,GHz, empleando una estructura periódica en su banda prohibida con simetría de deslizamiento para implementar el filtro en múltiples láminas metálicas delgadas apiladas sin contacto eléctrico entre ellas. El filtro se basa en cavidades apiladas verticalmente que utilizan el modo TE$_{103}$, lo que ofrece una mayor robustez frente a errores de fabricación y montaje. El filtro propuesto mantiene bajas pérdidas en el rango de frecuencias de 88-94\,GHz, incluso con variaciones de separación entre láminas de hasta 20 micras. El filtro se fabrica mediante corte por láser, con lo que se consigue una baja rugosidad superficial y una gran precisión dimensional. Las mediciones experimentales muestran una excelente concordancia con las simulaciones y demuestran la posibilidad de conseguir filtros de altas prestaciones en frecuencias de ondas milimétricas, manteniendo una baja complejidad y coste de fabricación mediante el uso de la tecnología de guía de onda multicapa combinada con el corte a láser.

This article presents a novel 3D-printed, self-supported coaxial-line X-band filter design. The filter is intended for Earth Observation (EO) data downlink systems, where it must effectively reject signals in a wide frequency range. The filter design incorporates a smooth-profile low-pass filter structure integrated with a short bandpass section with four λ/4 short-circuited stubs. The low-pass section design is optimized by means of shape deformation, including the inner and outer coaxial conductors, and leads to a wide rejection band up to around 40 GHz, to suppress undesired out-of-band frequencies. A prototype was fabricated in one piece using selective laser melting (SLM) and measured, showing excellent agreement with simulations, thus fulfilling the requirements of the target application.

Este artículo presenta el diseño de una antena de lente geodésica metálica integrada con una lente plano-convexa conformada y un polarizador dieléctrico anisotrópico en su apertura. Esta antena está pensada para aplicaciones en ondas milimétricas en la banda Ka (22-40 GHz). La configuración proporciona alta directividad y polarización circular dentro de una cobertura azimutal de ±56º. La lente geodésica está diseñada con 11 puertos de entrada en un extremo y una apertura radiante continua en el otro, dirigiendo el campo electromagnético desde cada puerto de entrada hacia direcciones espaciales específicas, generando así 11 frentes de onda planos distintos en el plano azimutal. La lente dieléctrica plano-convexa en la apertura de la antena colima el plano de elevación, mejorando la directividad de la antena. Además, un polarizador dieléctrico anisotrópico convierte la onda polarizada verticalmente de la lente geodésica en una polarización circular. La antena presenta un ancho de banda relativo del 38,6% (AR < 3 dB), habiendo sido completamente prototipada mediante fabricación aditiva.

En este artículo se propone un método de diseño de filtros microstrip en 3D. El método es válido para cualquier función de transferencia todo-polos y emplea una técnica de síntesis de inverse scattering para generar un perfil de impedancia que se implementa variando suavemente la altura del sustrato y la anchura de la tira conductora. De este modo, se pueden conseguir excursiones de impedancia característica mejoradas, lo que permite sintetizar filtros con bandas de rechazo anchas, profundas y dimensiones físicas compactas. Como ejemplo, se diseña un filtro paso bajo con frecuencia de corte de 8 GHz y banda de rechazo centrada en 16 GHz, con una longitud física de 21.96 mm. El filtro se simula utilizando CST MWS y las respuestas en frecuencia obtenidas confirman su excelente rendimiento.

En este trabajo se estudia el efecto multipactor (MP) en filtros paso banda implementados en tecnología groove gap waveguide (GGW), basados en cavidades rectangulares e iris de acoplamiento inductivo. Para el diseño efectivo del filtro GGW considerado, se ha estudiado primero una estructura equivalente en tecnología de guía de onda rectangular (RW) estándar, utilizando herramientas muy eficientes para calcular su respuesta eléctrica y los niveles de potencia umbral MP. A efectos de validación, se han fabricado dos prototipos de los filtros paso banda GGW y RW, diseñados para operar a 17,5 GHz (para aplicaciones de enlaces descendentes de satélite en banda Ka-band). Ambos están hechos de aluminio, cuyas propiedades de emisión de electrones secundarios se han tenido en cuenta, utilizando las herramientas informáticas disponibles, para predecir los niveles de potencia umbral de MP. Se ha logrado una buena concordancia entre todos los resultados simulados y experimentales.

This paper introduces an enhanced transition from microstrip to Empty Substrate Integrated Coaxial Line (ESICL). The new design eliminates most metallized vias and simplifies the upper intermediate layer, streamlining the manufacturing process. These modifications result in improved insertion losses and allow for the use of various substrate materials and thicknesses. The proposed transition's performance has been experimentally validated with two back-to-back prototypes. Measurement results show insertion losses below 0.4 dB and return losses exceeding 20 dB.

This paper presents the solution implemented in the S-band receiver of the Yebes Observatory, which was saturated by numerous radio frequency interferences (RFI). To

solve this problem, a high temperature superconducting filter with high selectivity, of order 10, based on the coupling of spiral resonators, was installed at the input of the low noise amplifiers. This filter allows operation in the linear region without reducing the receiver performance, thanks to its exceptional characteristics.

This paper presents a novel microstrip ridge gap waveguide (MRGW) N=2 coupled line microwave filter design using nematic liquid crystal (LC) as a substrate and thanks to LC’s dielectric anisotropy properties, the resonance can be easily controlled using an external electric or magnetic bias field. The filter is designed at 13 [GHz] using the coupling matrix method. We report the simulated tunability of 9.50-14.95 for two of the commercial LC mixtures (LC-1, LC-2). The merging of the MRGW technology and the LC technology can potentially contribute to the denser packaging of modern RF devices, improve insertion losess (IL) as well as frequency tunability.

En este trabajo se han analizado exhaustivamente las tolerancias de fabricación de la tecnología CLAF-SIW para aplicarlas al filtro conseguido en [1]. El filtro consiste en un BPF de cavidades apiladas en el rango de frecuencias milimétricas, la tecnología se adapta muy bien a este tipo de filtros y en ese rango de frecuencias. Aún así, hay que tener en cuenta las tolerancias en la fabricación. Se ha conseguido determinar los posibles errores en simulación, sobre la celda unidad EBG de la tecnología, sobre las dimensiones de los iris y cómo afectan en su conjunto al filtro. Posteriormente, se han analizado las tolerancias en medida, para conseguir mitigarlas y obtener la respuesta ideal del filtro.

En este trabajo se presenta un nuevo convertidor de modo TE10–TE20 para guías de ondas rectangulares (RW). La estructura propuesta se concibe como un único dispositivo sólido que se inserta en una sección recta vacía de una RW para obtener la conversión de modo deseada. El convertidor de modo diseñado se fabrica mediante técnicas de fabricación aditiva y dos materiales dieléctricos con diferentes permitividades. El trabajo incluye consideraciones teóricas para las dimensiones del diseño propuesto. Para validar la novedosa topología sugerida, se diseñó un convertidor de modo TE10–TE20 para su inserción en una sección recta vacía de 70 mm de longitud de WR-137. Los resultados simulados muestran que la pureza de modo es superior al 98 % para un rango de frecuencias entre 9.5 GHz y 11.6 GHz, mientras que la eficiencia de conversión es superior al 85 % para un rango de frecuencias entre 10.1 GHz y 11.7 GHz. El convertidor de modo fabricado se caracterizó en una configuración back-to-back utilizando transiciones de WR-90 a WR-137. Las medidas concuerdan satisfactoriamente con las simulaciones electromagnéticas. Además, se comprobó el comportamiento del prototipo fabricado midiendo el diagrama de radiación de una apertura WR-137 alimentada con el modo TE20 generado por el convertidor de modo fabricado.

This paper presents initial research on differentiable solvers for electromagnetics based on Automatic Differentiation (AD), aimed at efficiently integrating forward solvers into gradient-based optimization workflows and neural network training. Specifically, we explore differentiable programming techniques applied to two electromagnetic problems: parameter estimation in a simple RC circuit governed by ordinary differential equations (ODEs), and reflection coefficient computation in multilayer electromagnetic wave propagation. We systematically compare FiniteDiff.jl and two AD libraries ---ForwardDiff.jl and Zygote.jl--- in the Julia programming environment, evaluating their performance and precision in computing derivatives and gradients. Results highlight Zygote's superior efficiency and scalability, particularly advantageous in large-scale inverse problems involving numerous parameters. The proposed approach demonstrates significant potential for addressing complex inverse electromagnetic problems through differentiable programming paradigms.

This paper presents a systematic assessment of four machine learning (ML) models used for the simultaneous extraction of complex permittivity (𝜺) and permeability (𝝁) in magnetodielectric composites. Results are analyzed by focusing on metrics and techniques to improve models explainability and identify the main characteristics involved in the predictions. The models have been trained with 2554 samples obtained from full-wave simulations in CST microwave studio. The best model has been chosen using MSE and R<sup>2 metrics. An analysis of explainability has been performed to enhance understanding of the results and to establish feature importance in the model predictions.

This article describes the design procedure of a “filtenna” (filtering antenna). The “filtenna” is conceived as a third order filter consisting of two open ring resonators which are coupled to a resonant radiating patch through an aperture. The radiating patch behaves as the third resonator of the filter. The “filtenna” is used as the building block of a dual-polarization “diplectenna” (diplexing antenna). In particular, four pairs of coupled open ring resonators are connected to two radiating microstrip patches. Two of the pairs of coupled rings excite the radiation of the two patches in horizontal linear polarization at two different bands, while the other two pairs excite the vertical linear polarization at those bands. One of the patches radiates at a center frequency of 5.5 GHz, while the other patch radiates at a center frequency of 9.0 GHz. The “diplectenna” shows a fractional bandwidth of roughly 6.5% in both bands for both polarizations with sharp frequency selectivity, gain values larger than 7 dBi and cross-polar radiation levels below -20 dB.

This contribution presents a practical proposal for the analysis and visualization of satellite signal coverage using the Iridium constellation as a reference scenario. By modeling the orbital geometry of the satellites and the radiation pattern of their antennas, students can compute the received power on the ground and represent it over a geographic map. The activity is implemented in MATLAB using the Satellite Communications Toolbox and allows students to reinforce key concepts related to radio link modeling, such as antenna gain, propagation losses, and free-space transmission equation, within the context of a real low Earth orbit (LEO) system.

En este trabajo, se propone una metodología que combina el aprendizaje cooperativo y el aprendizaje basado en juegos como alternativa a la docencia expositiva en clases teóricas. Para sistematizar la aplicación de esta innovación y evaluar su impacto real sin sesgos, se ha decido utilizar una aproximación basada en el proceso de investigación-acción. Los resultados obtenidos son prometedores y muestran la capacidad de la metodología propuesta para mejorar diferentes aspectos del proceso de aprendizaje.

This communication describes the study and evaluation of low-cost RF measurement instruments intended for educational use. To this end, a separate analysis of the principles of operation is included for each type of typical RF test-equipment (i.e., a function generator, a spectrum analyzer, and a vector network analyzer). Then, an evaluation of the performance of these instruments is conducted for measurements in undergraduate laboratory experiments (e.g., transmission lines, characterization of antennas and/or passive filters). The values of some characteristic parameters are confronted with measurements made with high-performance commercial RF equipment. In conclusion, reasonable accuracy can be achieved using low-cost equipment. Thus, the use of low-cost RF instrumentation is validated to increase educational activities related to hardware testing, which has a positive influence on learning quality.

When learning analog and digital communications, students often remain in a theoretical environment, missing out on the practical aspects of wireless applications. Fortunately, the growing use of software-defined radio (SDR) devices is bridging the gap between what students learn and what they will face in industry. In this work, an app-based platform for transmitting and receiving signals using two SDR devices is presented. Students will be able to generate and transmit a basic signal with a message encoded. Then, upon receiving the signal, they will be able to interactively correct frequency and phase offsets before demodulating and decoding the message. This platform gives a baseline understanding of practical wireless communications systems and the impairments these real-world applications have.

This article presents a collaborative initiative between professors of Telecommunications Engineering and Nautical Science, with the objective of providing students with multidisciplinary and transversal training. The collaboration focuses on marine radars, a topic that is common to both degrees, but approached from different perspectives. For Telecommunication Engineering students, the initiative aims at incorporating operational and functional aspects in real contexts into theoretical design tasks; for Nautical Science students, it looks for relating the usual radar operation to further theoretical foundations, and to better understand the radar performance for different configurations, scenarios and goals. The teaching methodology is based on joint sessions between professors and students of both degrees, in order to share teaching approaches and laboratory equipment. This initiative has been conducted during eight-courses, with a positive evaluation from professors and students.

This paper presents the design and measurement results of a high-power, ultra-wideband amplifier based on the recently available 150-nm GaN-on-SiC process technology offered by Leonardo foundry. The designed power amplifier (PA) adopts a single-stage non-uniform distributed PA topology comprising ten active devices within a 5×5 mm2 die. To facilitate future system integration, the PA prototypes have been validated in three configurations: on wafer, wire-bonded to a test fixture, and packaged into a plastic QFN. The obtained results of the on wafer and bare die tests show that the designed PA can deliver an average output power higher than 39 dBm from 4 GHz to 18 GHz, with an average associated power added efficiency of 20 %. This amplifier has been designed to validate this new European manufacturing process and demonstrate its potential for the development of components for future radar and electronic warfare systems.

High electron mobility transistor (HEMT)-based amplifiers hold the state-of-the-art in cryogenic low-noise performance, but their reactive input impedance imposes a stark trade-off between input return loss and optimum noise match, making them non-ideal for wide-band designs at sub-GHz frequencies. Meanwhile, SiGe heterojunction bipolar transistor (HBT)-based amplifiers have the ability to span multi-decade bandwidths that reach close to DC, while having also been proven to be a compelling alternative for cryogenic low-noise designs in the low-GHz range. With previous work having shown some mass-produced commercial-off-the-shelf (COTS) HBTs to excel in the low-noise realm, the possibility of using commercially available devices for cryogenic low-noise is explored further, resulting in a 0.3-3.3 GHz SiGe HBT-based cryogenic low-noise amplifier (CLNA) incorporating bare-die devices from a European foundry achieving 6.4 K average noise temperature and 34 dB gain with |S₁₁| better than -9.7 dB when measured at 17 K.

This work explores the capability of nano-diodes fabricated in AlGaN/GaN heterostructures, controlled by a gate electrode, to operate as zero bias (current or voltage) detectors

at room temperature, by means of on wafer characterization up to 43 GHz. These devices are usually referred as Gated Self-Switching Diodes (G-SSDs). A quasi-static analytical model based on the measured DC curves is able to predict the behavior of the device at low frequencies (1 GHz). The current responsivity shows a maximum for a gate voltage just above the threshold when working as zero voltage detector in drain injection (DI) configuration. The frequency performance of the G-SSDs has been evaluated when working both as current and voltage detector and also when the RF power is injected in the gate port (GI). The potential to operate at higher frequencies has been validated up to 300 GHz in free space.

The RAEGE project, a collaboration between Spain and Portugal, aims to establish a geodetic VLBI network of radiotelescopes with cryogenic low-noise 2-14 GHz receivers as part of the VGOS initiative, enhancing space geodetic measurements with millimeter-level accuracy. Additionaly, in the framework of BRAND-EVN project, broadband low-noise receivers covering 1.5–15.5 GHz for radioastronomy VLBI have been developed, incorporating frequency converters compatible with DBBC3 backends. This paper presents the design, fabrication, and characterization of frequency downconverters for these receivers, focusing on the so-called B-band unit, which downconverts the 4–8 GHz band to an intermediate frequency range (DC–4 GHz). The design employs microstrip technology and precision-machined enclosures to ensure optimal impedance matching, gain control, and minimal noise contribution. Performance evaluation, including S-parameters, gain, P1dB, and noise figure measurements, confirms compliance with VGOS and BRAND specifications. The results validate the downconverter’s efficiency and underscore key advancements in broadband signal processing for both astronomical and geodetic VLBI applications.

En este trabajo se describen los parámetros de diseño, pruebas experimentales y simuladas de un prototipo experimental ArcSAR (Arc-Scanning Synthetic Aperture Radar) embarcado en un vehículo aéreo no tripulado para detección de blancos mediante el escaneo de un entorno permitiendo la localización de estos y evitar posibles obstáculos. Este prototipo que trabaja en bandas milimétricas (24GHz), permite sintetizar la apertura del tamaño de una antena de gran diámetro, a partir del ancho del haz de una antena de diámetro pequeño, característica que le posibilita tener una alta resolución acimutal para discriminación de blancos muy cercanos unos de los otros.

A partir de la evolución y mejora de prototipos ArcSAR terrestres diseñados por el grupo de Microondas y Radar de la Escuela Técnica Superior de Ingenieros de Telecomunicación de la Universidad Politécnica de Madrid, se realizaron modificaciones en lo relacionado a reducción de tamaño, disminución de peso y mayor autonomía, parámetros necesarios para que el prototipo ArcSAR pudiera ser embarcado en un vehículo aéreo no tripulado, mejor conocido como DRON.

This paper presents a Nolen 4x4 matrix beamforming network using lumped elements in the overall matriz; the main application is for the ISM 900 MHz band. The matrix proposed develops a solution with space reduction and good performance. The methodology for design branch line couplers and phase shifters is based on equivalence between transmission lines and lumped elements and it is depicted in the first place. We

fabricated a first prototype to 920 MHz as central frequency and we assembled the matrix over Rogers 4003 Substrate in one layer with lumped elements SMD type of 1005 package. The results show agreement with simulated results, the bandwidth obtained

was approximately 7.3 %; about the radiation patterns over output ports indicate good results in terms of beam scanning. The overall matrix size is 11.4 x 4.1 cm. Hence, this feeding network has the correct behavior for a Nolen 4x4 matrix and the footprint is seven times smaller than if it were developed using microstrip technology.

In this work, the wireless channel was measured in the FR3 band (7 to 24 GHz) using a vector network analyzer and virtual antenna arrays in an indoor environment, under both line-of-sight (LoS) and non-line-of-sight (NLoS) conditions. Path loss values were extracted from measurements conducted at multiple locations across the entire band, as well as within selected sub-bands: 7.125–8.4 GHz, 10–10.5 GHz, 10.7–13.25 GHz, 14.8–15.35 GHz, 17.7–19.7 GHz, and 21.2–23.6 GHz. For each case, the floating-intercept path loss model was fitted. Additionally, a partition loss model was implemented to estimate attenuation under NLoS conditions.

This study presents a mostly experimental work which explores the capabilities of the orbital angular momentum (OAM) waves for near-field (NF) indoors communications in the FR2 regions. With this goal, a well-known T-shaped unit cell is used with a circuital model and analytical expressions where, by changing the ratio of dielectric to air, it is possible to generate the necessary phase shifts to produce OAM waves. Once the transmitarrays (TAs) are designed, several tests are conducted where the orthogonality and the capability of avoiding objects of OAMs is explored. For this purpose, thanks to stereolithography, TAs are 3D-printed in our facilities and measured the orthogonality of the modes with their E-field pattern and the ability to pass through objects.

this paper presents the design and analysis of a self-oscillator type active integrated antenna using InGaAs HEMT technology with a feedback structure. The compact oscillator (1.5 × 2.6 cm²) is fabricated on a Rogers 4003C substrate and operates at 2.68 GHz. Harmonic balance simulations, employing the auxiliary generator technique in Advanced Design Systems, predict an output power of 11.519 dBm at 2.680 GHz. Measured results confirm a power output of 11.436 dBm at 2.681 GHz. Phase noise levels are -117.69 dBc/Hz at 1 MHz and -139.27 dBc/Hz at 10 MHz, validated using a spectrum analyzer (R&S FPL1026, 5 kHz - 26.5 GHz). The strong correlation between simulated and measured results confirms the accuracy and reliability of the proposed design, demonstrating its effectiveness in generating wireless signals without external excitation sources.

This communication contains the analysis and design of time-modulated arrays (TMAs) controlled by FPGA, and using cellular automata programs as a control sequence. It also includes a study of the implications of this implementation. The design and implementation of a 4-element TMA are performed with a working frequency of 2.22 GHz. The HMC550AETR switch commercialised by Analog devices is used for the inclusion of time modulation in the system through a control sequence generated by the FPGA Altera Cyclone III 3C16. Y Wilkinson power dividers and antennas that electrically behave like dipoles are incorporated to complete the design. Finally, the TMA is tested by means of the measurement of the received signal and the array factor over time, while rule 135 of the cellular automata is executed.

Este trabajo presenta el diseño y simulación, mediante el simulador electromagnético CST Microwave Studio Suite, de una antena compacta que opera a 2 GHz, destinada a su integración en una cápsula biomédica ingerible. El objetivo es demostrar una estructura miniaturizada que pueda incorporarse a un dispositivo de diagnóstico ingerible, similar a una cápsula médica, para futuras aplicaciones de monitorización gastrointestinal (GI) basadas en la interacción electromagnética. La antena está impresa en un sustrato RO3010 y alimentada por una sonda coaxial, totalmente encapsulada en una estructura de PLA biocompatible. Aunque las simulaciones se llevan a cabo en espacio libre, este trabajo sienta las bases para futuras aplicaciones de detección de anomalías tisulares mediante contraste dieléctrico.

The characterization of non-linear devices is a critical aspect of developing high-frequency circuits for wireless communication applications. However, conventional experimental techniques have predominantly relied on linear models, such as S-parameters, and figures of merit obtained under DC conditions to extrapolate the non-linear behavior at high frequencies. This approach has been constrained by the lack of suitable tools for experimentally assessing the frequency-dependent nonlinear response. In this work, we present a methodology based on non-linear dispersion parameters, specifically X-parameters, to analyze the non-linear behavior of graphene-based rectifiers as a function of their DC operating point, including self-bias effects. This approach, which can be extended to any nonlinear technology, enables a shift from purely DC-based metrics to a characterization framework that explicitly incorporates frequency dependence. The proposed technique offers a more accurate understanding of non-linear behavior, particularly in RF-DC rectification and frequency doubler applications.

The use of asymmetric coupled waveguides enables efficient management of losses associated with curvature. This type of geometry is particularly interesting in platforms such as silicon nitride, where radiation loss limits the bend radii that can be used and, consequently, the attainable density of integration. This document presents a review of recent results related to this configuration and its applications in racetrack-type microresonators, the design of ultra-compact polarizers, and biosensors.

In this work, we present the characterization of an integrated Distributed Bragg Reflector (DBR) laser designed for space applications. The laser delivers a high output power of approximately 2 mW and a continuous tuning range exceeding 100 GHz, with a side-mode suppression ratio (SMSR) of up to 49 dB, ensuring stable single-mode operation. These results highlight the DBR laser's potential as a critical component in advanced photonic systems, particularly for space-based and remote sensing applications that require stable, high-power, and tunable light sources.

La combinación de arrays con lentes dieléctricas es una solución atractiva para mejorar el rendimiento de la antena en aplicaciones de ondas milimétricas. El diseño y la optimización de estas lentes presentan retos importantes. Esto se debe principalmente a los altos requisitos computacionales de su simulación con paquetes de software de onda completa, debido principalmente a la simulación extra que se requiere para simular la distribución de fase no lineal del array. Una posible solución para acelerar el proceso de diseño es la aplicación de un método de trazado de rayos ("ray tracing'" RT en su denominación en inglés). Para hacer frente a las limitaciones de nuestro anterior modelo de RT en 2D, actualmente lo estamos ampliando para poder analizar escenarios 3D. En este trabajo describimos los pasos necesarios para la creación de la geometría y la implementación de la óptica geométrica dentro del modelo. La parte de óptica geométrica incluye tanto el RT inverso para la obtención de la distribución de fase como el RT directo para el cálculo del diagrama de radiación. Los resultados de nuestro modelo simplificado muestran una buena concordancia con modelos de onda completa.

ERMES 20.0 is the latest release of an open-source C++ finite element software designed to solve Maxwell's equations in the frequency domain. This version introduces new features, modules, and finite element formulations to address the complex challenges commonly encountered in the design and analysis of electromagnetic systems. Examples of ERMES 20.0 applications are: bio-electromagnetics, electrostatic discharges, electromagnetic compatibility, microwave engineering, and plasma-wave interactions. This paper highlights the key advancements in ERMES 20.0, detailing its new capabilities and demonstrating its potential to help in the numerical modeling and analysis of electromagnetic design problems.

The operation of various types of space plasma thrusters relies on heating the plasma with electromagnetic waves, typically in the MHz or GHz range. This is the case of electrodeless plasma thrusters.

To understand and characterize the propagation and absorption of electromagnetic power by the magnetoplasma, a commonly-used approach is to model the plasma as a linear, anisotropic, gyrotropic, dissipative medium based on the cold-plasma assumption.

Simulation codes ranging from finite differences (e.g. Yee scheme) to finite elements (e.g. Nédélec edge elements) are used to find the response of the wavefields to a given geometry, plasma density, and applied magnetic field profiles.

This presentation reviews recent efforts at Universidad Carlos III de Madrid to simulate electrodeless plasma thrusters with finite element schemes, and the occurrence of spurious wave solutions whenever the propagation regime includes so-called resonant cones. To characterize the spurious solutions, we set up a verification simulation case based on the Fresnel problem for a planar wave propagating in vacuum and into a plasma, and compare against the analytical solution. We find perfect agreement with our finite element solution, except for parametric regimes where the plasma has resonant cones.

Analysis of the analytical and numerical dispersion relations helps identify the sources of error, and potential countermeasures are proposed.

The study of electromagnetic waves propagation and plasma-wave coupling is a central aspect for the understanding of plasma thrusters performances, especially those driven by the excitation of radiofrequency waves, such as the Helicon Plasma Thruster. This work presents the design of a B-dot probe and its use for the characterization of the electromagnetic field patterns along the plasma plume ejected by a 450 W class helicon plasma thruster breadboard. The wave propagation results will be correlated with the thruster performances for a set of different operating conditions.

Como elemento clave en la observación de la Tierra mediante señales de oportunidad, la Reflectometría mediante señales de los Sistemas Global de Navegación por Satélite (GNSS-R) ha captado una creciente atención de la comunidad científica en las últimas dos décadas. El corto periodo de revisita y la resolución espacial moderada hacen que el GNSS-R espacial sea especialmente adecuado para monitorear cambios a gran escala en las aguas superficiales. Este artículo propone un nuevo método para la estimación rápida del almacenamiento de agua superficial (SWS, por sus siglas en inglés) mediante la combinación de la extensión y la profundidad del agua superficial. En este caso, la extensión del agua superficial se obtiene a partir de observaciones GNSS-R espaciales (mensuales, 0,01°), mientras que la profundidad del agua se deriva combinando la extensión del agua superficial con datos topográficos. Tomando la cuenca del Amazonas como área de estudio, se analizó la variación del almacenamiento de agua superficial en el Amazonas desde julio de 2019 hasta diciembre de 2024, y los resultados muestran una fuerte variabilidad estacional e interanual. Las comparaciones con la anomalía total de almacenamiento de agua terrestre (TWSA, por sus siglas en inglés) del Experimento de Recuperación de Gravedad y Clima (GRACE) y las mediciones de descarga fluvial por satélite muestran fuertes correlaciones (los valores de R fueron de 0,90 y 0,80, con desfases temporales de 1 y 2 meses, respectivamente). Esto demuestra la eficacia del método propuesto. Por último, también se identificaron posibles episodios de sequía en la cuenca del Amazonas a partir de 2023. Esta información sobre el almacenamiento de agua superficial, que puede actualizarse rápidamente, facilitará la realización de nuevos estudios y análisis hidrológicos.

Global Navigation Satellite System – Reflectometry (GNSS-R) can be used to estimate the surface soil moisture from the scattered GNSS signals, after correcting mainly for the surface roughness and vegetation effects. However, it is still a matter of debate how deep the signal at L-band can actually penetrate the soil as a function of the actual soil moisture profile.

To experimentally assess this, a network of 20 probes measuring soil moisture, temperature, and conductivity every 30 minutes from 5 to 115 cm was installed in la Fuliola, Lleida. Next to the field, PYCARO-2, a multi-constellation (GPS, Galileo, BeiDou, and GLONASS), multi-frequency (L1/E1/B1 and L2/E2/B2), and dual polarization (RHCP and LHCP) GNSS-R receiver, was installed in the top of a 10 m mast in July 2023.

In this work we analyze the multi-frequency and polarimetric GNSS-R observables and investigate their temporal evolution and dependence with the soil moisture and temperature profiles, surface roughness, as well as other vegetation and meteorological parameters.

This research introduces an innovative technique for subsurface soil moisture measurement using P-band LoRa Signals of Opportunity (SoOp). Accurate soil moisture monitoring remains a significant challenge in Remote Sensing, with conventional methods limited by installation requirements, restricted spatial coverage, and invasive measurement techniques. Our approach exploits the unique propagation characteristics of LoRa signals, which offer superior soil penetration depth than L1 or L5 GNSS signals, typically used in Global Navigation Satellite System Reflectometry (GNSS-R). Despite their relatively low emitted power (<30 dBm), LoRa signals transmitted from Low-Earth Orbits have demonstrated reliable reception by Earth ground stations. The reduced distance to Earth, and the spread spectrum characteristics of the modulation compensate for the lower transmission power, resulting in improved signal-to-noise ratios as compared to GNSS-based approaches. This novel methodology presents significant potential for advancing agricultural monitoring, environmental science, and climate research applications.

Los Enlaces Ópticos Inter-Satelitales (O-ISL) se enfrentan a enormes desafíos en la precisión del apuntamiento debido a los errores en la estimación de la posición del satélite derivados de los TLE. Estos errores incrementan el llamado Cono de Incertidumbre (UC), afectando la adquisición del enlace. Este trabajo propone el uso de un sistema híbrido en el que se utiliza el sistema de RF para mejorar la precisión del apuntamiento inicial mediante el intercambio de datos de posición más recientes y precisos, en lugar de depender únicamente de la propagación de los TLEs proporcionados con anticipación al establecimiento del enlace. Los resultados muestran que el uso del sistema de RF reduce significativamente el UC de 1,51 kilómetros, para los enlaces basados en TLE, a 17 metros, para el intercambio de datos de GNSS por medio de RF. Esta mejora optimiza tanto la precisión del apuntamiento como el tiempo de adquisición.

This paper presents an analysis of on-board computers (OBCs) used in CubeSats, focusing on their application in communication payloads. CubeSat missions require highly reliable, efficient, and adaptable OBCs capable of handling varying computational loads while operating in harsh space environments. The paper explores three main types of OBC architectures—microcontroller-based, FPGA-based, and hybrid systems—and their suitability for different CubeSat mission profiles. Additionally, the paper investigates the integration of communication payloads with OBCs, emphasizing key communication protocols such as I2C, SPI, SpaceWire, and emerging technologies like LoRa, NB-IoT, and 4G/5G networks. The selection of OBC architecture and communication protocol is critical to optimizing mission performance, power consumption, and overall mission success. Case studies of CubeSat missions are examined to illustrate the practical implementation of OBC architectures across various mission types.

Satellite constellation design faces significant challenges due to the interdependence of numerous technical and economic factors. Traditional approaches often focus on single aspects such as coverage or network architecture, resulting in suboptimal system designs. This paper presents COMPASS (COmprehensive Modeling Platform for Architecting Satellite Systems), an end-to-end optimization framework based on trade-space exploration that integrates five interconnected models: satellite mass and cost estimation, message transmission simulation, launch cost calculation, financial performance evaluation, and trade-space analysis. The simulator's capabilities are demonstrated through a messaging service use case based on LoRa technology, targeting global population without cellular coverage. Pareto analysis of 729 architecture alternatives reveals that satisfied demand plateaus at approximately 50%, indicating that further constellation growth becomes ineffective beyond certain configurations. Network performance analysis identifies system bottlenecks, while financial modeling confirms profitability even at low message pricing of $0.01 per message. COMPASS enables designers to identify optimal constellation architectures that balance technical performance with economic viability, significantly accelerating the design process.

En las últimas décadas, ha habido un aumento significativo del número de misiones de observación terrestre. Impulsado por la miniaturización de las cargas útiles y el incremento del uso de plataformas como nanosatélites, el acceso al espacio se ha facilitado considerablemente, abriendo las puertas a un mayor número de empresas e instituciones a realizar este tipo de misiones. Muchas de ellas requieren antenas de grandes dimensiones, siendo el desarrollo de antenas desplegables una tecnología clave para avanzar el estado del arte. Este trabajo presenta el diseño y validación electromagnética de una antena tipo lente de zonas de Fresnel desplegable, concebida para la misión 3Cat-8 del UPC NanoSat Lab, de la Universitat Politècnica de Catalunya. La validación presentada sigue los pasos de trabajos anteriores con la medición de un prototipo a escala de la antena. El avance de sistemas desplegables para nanosatélites, como antena, tiene el potencial de aumentar las capacidades de observación terrestre y/o de comunicaciones, siendo esta la primera antena lente de zonas de Fresnel diseñada para su uso en órbita.

This paper presents a planar microwave sensor implemented in microstrip technology and operating in transmission. The device is devoted to detecting tiny changes in the dielectric constant of the medium surrounding the sensing element (or material under test -MUT). Such sensing element is a dumbbell defect-ground-structure (DB-DGS) resonator, transversally etched in the ground plane. The operating principle of the sensor is the change in the phase of the transmission coefficient at a specific (operating) frequency caused by variations in the dielectric constant of the MUT. To achieve a high sensitivity, an inductive strip is placed between the access lines, on top of the DB-DGS resonator. By this means, closely spaced resonance and antiresonance frequencies are generated, with the result of a high phase slope in between, a necessary condition for sensitivity enhancement. The maximum sensitivity of the reported prototype is -66.8º per unit of dielectric constant variation, and the figure of merit, or ratio between the maximum sensitivity and the area of the sensing region expressed in squared wavelengths, is FoM = 6243º/λ².

Este trabajo presenta un sensor resonante planar de microondas para medida de concentración de alcohol (etanol y metanol) en agua. El diseño del sensor se basa en la concentración de la energía eléctrica en la región de la muestra mediante un condensador interdigital y una línea de alta impedancia, sin plano de masa, formando una estructura semi-lumped. La respuesta en frecuencia del sensor se puede describir mediante un modelo circuital de elementos concentrados . El sensor se ha estudiado experimentalmente con disoluciones de etanol y metanol en agua, con mejores resultados en términos de sensibilidad para el etanol, en coherencia con las frecuencias de trabajo del sensor, más próximas a la región de relajación del etanol. Las sensibilidades experimentales para tres medidas (frecuencia de resonancia, ancho de banda a 1 dB y nivel mínimo de transmisión), alcanzan valores máximos respectivos de 3,0 MHz/%, 3,67 MHz/% y 0,069 dB/% para el etanol, y de 1,1 MHz/%, 2,10 MHz/% y 0,039 dB/% para el metanol.

Hidden Markov Models (HMMs) have proven to be powerful tools for modeling sequential data across various applications. This paper explores their use in RFID-based tag detection, focusing on improving accuracy and robustness in environments affected by signal noise and interference. We propose a methodology that leverages the probabilistic nature of HMMs to classify and predict RFID tag readings, thereby enhancing detection reliability. The effectiveness of the approach is evaluated through simulations, demonstrating its potential as a cornerstone for improving modern RFID reader performance. Our results indicate that HMMs can significantly reduce inaccuracies, providing a more reliable solution for RFID applications. Additionally, we analyze the impact of model parameters and propose optimizations to enhance performance in dynamic scenarios. This research contributes to the advancement of intelligent RFID systems by integrating probabilistic models for improved tag detection and identification.

In this work, we present an RFID-based indirect soil moisture sensor based on the application of Machine Learning. More specifically, we suggest an unsupervised approach that does not require information about the real height and moisture levels. This approach can be of great interest in practical agricultural deployments, where the careful deployment of tags at specific depths within the soil is challenging. It allows an estimation of the posterior probability of moisture, based on the available Received Signal Strength Indicator (RSSI) and phase. The suggested method enables the RFID system to operate as a sensor by probabilistically quantifying measurement uncertainty, which is a key distinction from existing methodologies. In this paper, we focus on two differentiated moisture cases to show the validity of our approach. Future research will extend the proposed methodology to a wider set of moisture levels.

This paper presents a highly sensitive microwave sensor for bioparticle detection, designed around a ring-gap resonator integrated with a microfluidic channel. The sensor's structure is optimized to enhance electric field confinement, improving its sensitivity to dielectric variations. Experimental validation using commercial microbeads as bioparticle models demonstrates clear resonance shifts, confirming the sensor's capability for precise detection of particles up to 5 µm. These results highlight the potential of the proposed approach for real­time, label-free biosensing applications, offering a promising tool for biomedical diagnostics and analytical chemistry.

With the accelerated growth of online transactions, counterfeiting of various products, such as pharmaceuticals, textiles, and food items, has increased. This work proposes the use of non-cloneable authentication labels for product protection, combining the substrate used and its geometry to obtain a unique spectral response. The labels are manufactured in two steps. In the first, a laser-induced graphene (LIG) layer is formed, which can be implemented using a laser (e.g., CO2 laser) to directly convert various precursors (e.g., polyimide) into graphene. The second step involves an electroplating process that generates traces with variable sheet resistance according to manufacturing parameters. A prototype of a scanner designed to characterize the electromagnetic spectrum is also presented. Results obtained with simple resonators and complex patterns demonstrate the feasibility of this technology.

This paper presents a preliminary investigation into the relationship between UHF RFID signal characteristics (Received Signal Strength Indicator - RSSI and phase) and the vertical distance between the reader antenna and a water surface. Due to experimental constraints preventing direct soil moisture measurement, the study was adapted to use a 50-liter container filled with water, varying the reader height and transmission power. Initial manual data inspection revealed an apparent linear relationship between the signal phase and reader height, as well as between phase and the volume of water added (affecting water level). We outline the modified experimental methodology and propose the use of Feedforward Neural Networks (FFNN) for baseline modeling and Sparse Gaussian Process Regression (SGPR) to model the observed relationships and quantify measurement uncertainties efficiently. This work serves as a foundational step towards developing robust RFID-based liquid level or moisture sensing techniques, providing a methodology for controlled experimentation and data analysis using scalable probabilistic machine learning models. Data and code are intended for release via a public repository.

Planar microwave sensors have become very popular for early detection of anomalous samples. The resolution of these sensors can be improved applying loss compensation through an active feedback loop, and a systematic and precise design of these sensors can be performed based on stability analysis of feedback systems. This paper proposes a standalone oscillator-based active sensor formed by a Complementary Split-Ring Resonator (CSRR) and a Colpitts oscillator. These components have been designed according to the Normalized Determinant Function (NDF) for operation at the single frequency of 3 GHz, and good agreement has been obtained with the spectral response obtained through non-linear simulation. The sensing capability of the oscillator has been tested evaluating the impact of increasing the permittivity, observing a significant resolution improvement. However, the limitations in the dynamic range of the sensor hinder the detection of variations in losses. Experimental results will be presented at the conference.

La identificación y localización de la abeja reina en el interior de una colmena es fundamental para la reproducción y el funcionamiento de la colonia. Tradicionalmente, la localización de la abeja reina se ha realizado de forma tediosa mediante inspección visual de cada uno de los panales de la colmena, diferenciando a la abeja reina del resto con una marca de pintura en el tórax. Recientemente, se han desarrollado etiquetas RFID con un tamaño adecuado para ser pegado en el tórax de una abeja, lo que podría permitir tanto su identificación como localización de una forma más eficiente. En este trabajo se han llevado a cabo medidas de cobertura de un sistema RFID en la banda de UHF con una etiqueta situada el interior de la colmena en diferentes posiciones en cada panal y con la antena del lector localizada en el exterior de la colmena. Los resultados muestran que, si hay cobertura, la etiqueta podría ser localizada con una incertidumbre de 2 panales.

Este trabajo presenta el diseño y la evaluación de una agrupación de antenas cilíndrica para lectores RFID en la banda UHF, compatible con las normativas ETSI, FCC y las bandas WiFi de 2.45 GHz. La agrupación está compuesta por 12 antenas monopolo de banda ultraancha (UWB), dispuestas en una configuración de 6×2. Se introduce un plano de tierra en forma de U para mejorar la directividad sin comprometer el ancho de banda. La celda unidad, fabricada sobre un sustrato FR-4, fue optimizada y replicada para formar la agrupación completa. Simulaciones electromagnéticas de onda completa realizadas en CST Studio Suite confirman el buen acoplamiento de impedancia y la reducción del acoplamiento mutuo. La agrupación alcanza un ancho de banda del 37.9 % entre 800 MHz y 1.15 GHz, con niveles de acoplamiento mutuo inferiores a –15 dB en todas las bandas de operación RFID. El control del diagrama de radiación se demuestra mediante la excitación de diferentes puertos, alcanzando valores de directividad de hasta 6.87 dB y una eficiencia total de 0.55 dB. Estos resultados validan la idoneidad de la agrupación para una detección robusta y flexible de etiquetas RFID en entornos electromagnéticos complejos.

This communication presents the design and comprehensive evaluation of an RFID reader antenna tailored for UHF applications (868-915 MHz). The proposed design incorporates a metallic rectangular cavity, two arc-shaped planar feeding elements, and an annular slot extruded on the upper surface of the cavity. By combining these elements, the antenna achieves an operational bandwidth of 11.4 % and a directivity of 8.13 dBi at 868 MHz and 8.49 dBi at 915 MHz. Moreover, the antenna consistently maintains an axial ratio below 1.6 dB at both frequencies, ensuring excellent circular polarization performance. The radiation pattern's 3 dB beamwidth exceeds 71 degrees, which provides a wide coverage area suitable for complex communication environments. These performance characteristics demonstrate that the proposed antenna design is highly effective for enhancing the reliability and efficiency of RFID systems in various industrial and logistics applications.

Quantum Rydberg atom-based radio frequency (RF) sensors exploit the exceptional sensitivity of highly excited atomic states to detect electromagnetic fields with very high precision, offering potential advances in telecommunications, radar and microwave radiometer systems, GNSS-Reflectometers, and electromagnetic compatibility testing. This study presents a detailed MATLAB simulation analysis of radio-frequency sensors modeled as a five-level rubidium-87 (Rb-87) system under the influence of RF and optical fields. The simulation leverages the Lindblad master equation to capture the coherent evolution, the spontaneous emission, the collisional dephasing, and the field-induced ionization. For an external RF electric field of E0 = 100 mV/m, a frequency sweep from 10MHz to 10GHz reveals the impact of noise: an ideal case just limited by quantum noise yields a sensitivity of 0.01 μV/m/√Hz and a SNR of 177dB, while for E0 = 10 mV/m and a realistic noise (−130 dBm/Hz) the sensitivity worsens to 72 − 633 μV/m/√Hz and a SNR of 72 dB. The study investigates the effects of RF field amplitude, atom density, and environmental parameters such as residual magnetic field and ambient temperature, in the sensitivity and bandwidth of these promising receivers, offering a framework to optimize Rydberg-based sensing technologies for Earth Observation, Communication and Navigation systems.

This work highlights the influence of sideband impedance on the stability of RF power amplifiers. A reconfigurable measurement setup is developed, allowing independent control of baseband and sideband impedances to experimentally assess their impact on stability. The proposed methodology employs the large-signal stability parameter, K</sub>LS</sub>, to predict instability under various baseband impedance conditions. Experimental results demonstrate that, even when the amplifier is matched at its fundamental frequency, certain sideband impedance combinations can trigger oscillations, as observed in a fabricated GaAs based microstrip amplifier. By correlating measured scattering parameters with the predicted K</sub>LS</sub> values, stable operating conditions are identified. The results emphasize the necessity of considering sideband impedance in power amplifier stability analysis to prevent undesired oscillations.

Esta comunicación describe el diseño de un amplificador de potencia (PA) híbrido, adecuado para el uso de modulación de carga (load modulation). El diseño está optimizado para aplicaciones a una frecuencia de 3.5 GHz y específicamente pensado para comunicaciones con vehículos aéreos no tripulados (UAVs). El diseño utiliza un transistor de alta movilidad de electrones de nitruro de galio (GaN-HEMT), seleccionado por su superior potencia y eficiencia, un factor crucial para aplicaciones embarcadas. Se basa en una configuración de amplificador balanceado (BA), que combina dos amplificadores de potencia individuales mediante acopladores. Los acopladores se diseñan utilizando "curvas de llenado de espacio" para mejorar la potencia mientras se minimizan las reflexiones de señal. El circuito puede operar como un BA convencional o como un amplificador balanceado modulado por carga (LMBA). El circuito diseñado fue fabricado y medido. En el punto de compresión P2dB, se midieron: una potencia de salida de 34.5 dBm, una ganancia de potencia de 15 dB y una eficiencia en el drenador cercana al 40%.

In this paper, we demonstrate the improvement in circuit performance when time-varying circuits are modulated by non-sinusoidal waveforms. Specially we focus on triangular and rectangular modulations. By this, bandpass filters are designed and compared to conventional cases in order to exhibit the enhancement. Specially, the bandpass filters are desined to invoke non-reciprocity, an exotic and very interesting feature in time-modulated systems. A method of analysis based on the spectral domain is employed, establishing a general approach that is valid and applicable to other types of signals, as long as it is possible to obtain its decomposition in Fourier series. The results obtained from our model match those simulated using the Keysight ADS, thus validating the present approach.

Este trabajo presenta la integración de un sistema receptor de satélite en banda Ka basado en componentes comerciales disponibles en el mercado (COTS). El receptor consta de un amplificador de bajo ruido, un filtro pasa banda, un mezclador subarmónico, un sintetizador de frecuencia y un amplificador de frecuencia intermedia (FI). La banda de frecuencias del receptor es de 27 - 30 GHz, siendo una de las bandas asignadas a las comunicaciones Satcom para enlace de usuario. La banda de FI es DC - 2.5 GHz, que se establece mediante el rango de operación del mezclador. Todos los COTS seleccionados son circuitos integrados monolíticos de microondas (MMIC), excepto el sintetizador de frecuencia, que está compuesto por un MMIC encapsulado. Se ha diseñado un chasis a medida para integrar el receptor, que sirve como precursor de la integración de estos componentes en un módulo System-in-Package (SiP) para su evaluación en aplicaciones espaciales. El primer objetivo del sistema desarrollado en formato convencional (chasis) es caracterizar y validar la funcionalidad de los componentes COTS como receptor de banda Ka. Este enfoque va más allá de la simple conexión de estos componentes; implica planificar cuidadosamente el diseño estructural del chasis en el menor espacio posible.

The current responsivity of zero-bias microwave detectors based on FETs is assessed for the case of a GaN HEMT by means of Monte Carlo (MC) simulations and a small-equivalent circuit (SSEC). A MC analysis is presented at very intrinsic level, including RF power reflection and transmission effects. Optimization of the detector is proposed using the SSEC and a circuit simulator in order to study the impact of parasitic elements. An analytical expression for the responsivity allows us to incorporate the effect of adding external Csub<gs> and Csub<gd> capacitors. The inclusion of these elements in the layout may improve the bandwidth in fabricated detectors.

This work presents a monolithic transmit/receive (T/R) frontend for the 6–18-GHz band, implemented in 150-nm gallium-nitride (GaN) technology. Single-die integration is leveraged by co-designing all subcircuits: the T/R asymmetric switch simplifies the transmit (Tx) path to save for Tx output power and efficiency, while its receive (Rx) branch merges into the low-noise amplifier input matching network for compactness and reduced noise. On-wafer measurements show an average Tx output power of 9.5 W (minimum of 5.6 W) with 19.4 % efficiency (minimum of 13.5 %) across the band. In Rx mode, the prototypes exhibit over 21 dB gain with an average noise figure of 3 dB (maximum of 3.3 dB). These metrics compete with the state of the art of ultrawideband GaN-based single-chip T/R frontends.

This paper presents a comparative analysis and propagation modeling of path loss (PL) in terahertz (THz) channels for indoor scenarios at 300 GHz. Experimental measurements in a conference room are used to evaluate several literature-based PL models by comparing their root-mean-square error performance. A custom-developed three-dimensional ray-launching simulation tool is introduced and validated against measurement data, yielding a mean absolute error of 0.77 dB. Furthermore, the study examines the impact of receiver height on PL characteristics by applying the Close-In PL model across multiple vertical levels of the conference room, revealing significant variations in the PL exponent and standard deviation. These findings underscore the need for height-specific channel models to support the design of robust THz communication systems for next-generation networks.

Intelligent systems increasingly leverage contextual data, such as air quality or user location, to provide enriched, context-aware services. The widespread use of IoT devices, along with advancements in computational capabilities and deep learning, is driving the development of more complex systems supporting diverse applications. However, these context-aware environments present challenges related to interoperability, scalability, and device/platform heterogeneity. Addressing them requires a structured approach, defining a set of software entities running across different contextual units and information systems that function as data collectors and aggregators. These units may employ from simple decision rules to state-of-the-art machine learning techniques to acquire knowledge and can potentially operate as distributed intelligent agents. A critical aspect of such systems is secure communication between these software entities: robust authentication, integrity, and confidentiality mechanisms are essential to maintaining system trust. This article explores the challenges of secure communications in complex, agent-based, context-aware scenarios. Moreover, it also reviews technologies to ensure confidentiality, integrity, and authentication.

The integration of cognitive systems and ambient intelligence has led to significant advancements in user-adaptive environments, particularly within Ambient Assisted Living applications. Audio-based interactions provide an intuitive and efficient means of communication, enabling a broad range of cognitive and assistive services. However, these advancements introduce substantial security and privacy concerns, particularly when processing and storing the associated data. This article presents a preliminary approach to audio-based authentication, utilizing machine learning techniques to enhance security in cognitive environments by ensuring accurate identification of individuals based on voice fingerprinting. Moreover, it outlines a data protection strategy and discusses privacy-preserving mechanisms to ensure compliance with ethical and regulatory standards.

Este trabajo presenta una solución innovadora basada en la computación Edge y la inteligencia artificial para detectar en tiempo real conductas peligrosas en entornos urbanos multimodales. Las imágenes son procesadas localmente en dispositivos embebidos desplegados en la infraestructura urbana, evitando la transmisión de imágenes sensibles y garantizando plenamente la privacidad de peatones y vehículos según las normativas europeas y españolas (RGPD y LOPDGDD). Mediante modelos avanzados de aprendizaje profundo y técnicas robustas de seguimiento multiobjeto, el sistema genera analíticas anonimizadas y alertas de seguridad proactivas. La solución propuesta contribuye significativamente a mejorar la seguridad vial, la privacidad ciudadana y la gestión inteligente del tráfico dentro del paradigma de ciudades cognitivas.

This paper presents an approach for the periodic collection of environmental data using an autonomous heterogeneous fleet of Automated Guided Vehicles (AGVs). The system integrates SLAM-based navigation, a decentralized architecture leveraging ROS 2, and secure communication protocols to ensure resilience in cognitive environments. A deployment in a real-world university setting is discussed, highlighting system performance and validation results. The proposed solution enhances se-

cure data acquisition while maintaining adaptability to dynamic environments. Additionally, its modular and scalable design makes it particularly well-suited for cognitive environments, such as smart campuses or industrial testbeds, where autonomous perception, decision-making, and interoperability are critical.

This paper focuses on the importance of radio planning and assessment of industrial environments for the future Cognitive Industry and Industry 5.0. The current and most commonly used wireless communication technologies, such as those based on the standard IEEE 802.11, Bluetooth, ZigBee, UWB, LoRaWAN, SigFox or NB-IoT already pose significant challenges regarding coexistence, coverage/capacity and noise, and interference immunity in industrial environments. The implantation of new rising technologies (e.g., Mioty, WiFi HaLow), the deployment of 5G networks in such environments (for the use of complete 5G services or RedCap devices) and the new frequency bands coming with 6G networks will create much more complex industrial environments in terms of radio planning tasks. Considering that, this work presents a deterministic simulation tool for volumetric RF analysis of industrial environments, showing the relevance of such accurate tools for the development of the future cognitive industry based on reliable and resilient wireless communication systems.

Wearable devices have gained significant popularity recently due to their ability to collect vast amounts of physiological data non-intrusively. However, these devices' resource-constrained nature often prioritises their operations' efficiency while security considerations are overlooked. This paper identifies the security vulnerabilities of EmotiBit bracelets, an open-source wearable device commonly used in healthcare and education projects. To address concerns related to data confidentiality and device authentication within this ecosystem, we propose two security schemes based on pre-shared keys and public-key cryptography. Additionally, the paper discusses the details of the implementation of these schemes and provides an evaluation of their strengths and limitations.