Caracterización eléctrica y térmica de amplificadores MMIC de potencia

La aparición de numerosas y novedosas aplicaciones de comunicaciones, y la continua búsqueda de anchos de banda cada vez más elevados con el objetivo de garantizar mayores tasas de transmisión en sistemas de comunicaciones y mayor resolución en aplicaciones militares y radar, obliga a la aparición de sistemas trabajando en bandas de frecuencias reservadas hasta ahora para aplicaciones muy concretas y de corte casi exclusivamente militar (bandas X, K y superiores). Para garantizar requisitos de cobertura, calidad de la transmisión o detección de un blanco bajo determinadas circunstancias, estos sistemas, operando a frecuencias que superan los 10 GHz, precisan niveles de potencia en la señal transmitida cada vez más elevados. Los sistemas de microondas cuentan con transmisores de potencia capaces de garantizar el nivel de potencia de señal a su salida requerido por la aplicación. Estos transmisores están por lo general formados por una cadena de circuitos monolíticos de microondas (MMICs) debido a múltiples ventajas sobre otro tipo de tecnologías: bajo coste por dispositivo, prestaciones, fiabilidad, reducido tamaño, versatilidad, integración de múltiples y variadas funciones en un mismo chip... En esta tesis doctoral se presenta el diseño de dos prototipos de transmisor de potencia de microondas destinados a ser empleados como etapas de salida de un sistema radar de onda continua y frecuencia modulada por un lado, y un sistema transceptor completo para comunicaciones punto-multipunto por otro. El objetivo propuesto en este trabajo de tesis doctoral es la caracterización tanto eléctrica como térmica de los amplificadores monolíticos de potencia integrados en los prototipos de transmisor desarrollados. Este tipo de amplificadores de potencia es actualmente el elemento estrella en transmisores de estado sólido y el nivel de madurez que ha alcanzado la fabricación de dispositivos de efecto de campo o FET (field effect transistor) sobre sustratos de AsGa (arseniuro de galio), hace que sea ésta la tecnología generalmente empleada en los amplificadores de potencia MMIC comerciales actuales para bandas de microondas y milimétricas. El trabajo de tesis doctoral que se presenta aborda diferentes aspectos relativos a la caracterización eléctrica y térmica de amplificadores MMIC de potencia. Los resultados obtenidos a partir del estudio teórico y experimental llevado a cabo han contribuido a un mejor entendimiento del comportamiento de los amplificadores MMIC de potencia empleados, así como a un mejor diseño de los prototipos de transmisor desarrollados

Identidad profesional y conocimiento matemático para la enseñanza de maestros en formación

En este estudio se pretende obtener una mayor comprensión sobre la identidad profesional en formación de estudiantes para maestro y las implicaciones para los programas de formación del profesorado. Se indaga sobre las reflexiones realizadas por estudiantes para maestro de educación primaria concernientes a sus experiencias relativas a la enseñanza y aprendizaje de las matemáticas y a conocimientos que estiman necesarios para enseñar matemáticas. Los resultados obtenidos revelan los aspectos que estos estudiantes destacan como elementos constitutivos de la identidad profesional del maestro haciendo mención a los componentes propios del proceso de enseñanza y aprendizaje de las matemáticas. Se propone una aproximación de la caracterización de la identidad profesional a través del conocimiento matemático para la enseñanza

Razonamiento configural como coordinación de procesos de visualización

Presentamos un estudio que identifica los procesos de visualización de estudiantes para maestro, cuando resuelven problemas de geometría, que requieren una prueba matemática, en un entorno de lápiz y papel. Los resultados muestran la influencia que tienen las figuras iniciales, que acompañan a los problemas, y las modificaciones posteriores de estas figuras en el desarrollo de las aprehensiones discursiva y operativa, que constituyen los vínculos entre los procesos de razonamiento matemático y la visualización en la resolución de problemas de geometría en contexto de lápiz y papel. Finalmente, identificamos posibles causas de las limitaciones que dificultan el desarrollo de dichas aprehensionesThis study identifies visualisation processes in student primary teachers when they solve geometry problems requiring mathematical proof, in a pencil-and-paper environment. The results reveal the importance of the initial diagrams that accompany the problems, as well as subsequent modifications of these diagrams in the development of discursive and operative apprehension, constituting as they do links between mathematical reasoning processes and the visualisation of geometry-problem solving in a paper-and-pencil context. Finally, we identify the possible causes of those limitations that hinder the development of such apprehension

Phase sensitive low-coherence interferometry using microwave

We report on a low-coherence interferometer based on Microwave Photonics (MWP) which allows, for the first time to the best of our knowledge, stable determination of the interferogram’s phase. The interferometer is built on suppressed carrier, double-sideband modulation, dispersive propagation in a chirped fiber Bragg grating, demodulation by electrooptical frequency down-conversion, and suitable signal processing techniques to account for modulation impairments. Taking as a reference a direct normalization of the link’s microwave response, the system retrieves high-resolution interferograms, both in amplitude and phase and free from distortion induced by higher-order dispersion, in an optical path difference of 16.3 mm, surpassing previously reported values based on MWP implementations. We present representative applications targeted to the characterization of C-band sources and components, such as direct analysis of interferograms with 5.5 fs temporal resolution, Fourier-transform spectroscopy with 14 GHz spectral resolution, and optical low-coherence reflectrometry of the impulse response’s amplitude of fiber Bragg gratings with 0.55 m spatial resolution

Multilayered additive-manufactured half-wavelength coupled line filters

This work presents the design, fabrication and measurements of third-order multilayered filters by additive manufacturing technology. The filters are fabricated using conventional half-wavelength line resonators and a low-cost 3d polylactic acid polymer additive manufacturing process, which allows rapid prototyping and fabrication of complex topologies. The designs, performed at a centre frequency of 2.0 GHz, aim to provide fast manufacturing and get enhanced performances when compared to conventional coupled line third order filters using microstrip technology on commercial substrates. The simulated and measured responses of the fabricated prototypes are in all cases in good agreement

Low-Cost Additive Manufacturing Techniques Applied to the Design of Planar Microwave Circuits by Fused Deposition Modeling

This work presents a study on the implementation and manufacturing of low-cost microwave electronic circuits, made with additive manufacturing techniques using fused deposition modeling (FDM) technology. First, the manufacturing process of substrates with different filaments, using various options offered by additive techniques in the manufacture of 3D printing parts, is described. The implemented substrates are structurally analyzed by ultrasound techniques to verify the correct metallization and fabrication of the substrate, and the characterization of the electrical properties in the microwave frequency range of each filament is performed. Finally, standard and novel microwave filters in microstrip and stripline technology are implemented, making use of the possibilities offered by additive techniques in the manufacturing process. The designed devices were manufactured and measured with good results, which demonstrates the possibility of using low-cost 3D printers in the design process of planar microwave circuits

3D-Printed Electromagnetic Band-Gap Band-Pass Filter Based on Empty Single-Ridge Waveguide

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A novel band-pass filter based on a periodically drilled SIW structure

The design and fabrication of a band-pass step impedance filter based on high and low dielectric constant sections has been realized on substrate integrated waveguide (SIW) technology. The overall process includes the design of the ideal band-pass prototype filter, where the implementation of the impedance inverters has been carried out by means of waveguide sections of lower permittivity. This can be practically achieved by implementing arrays of air holes along the waveguide. Several SIW structures with and without arrays of air holes have been simulated and fabricated in order to experimentally evaluate their relative permittivity. Additionally, the equivalent filter in SIW technology has been designed and optimized. Finally, a prototype of the designed filter has been fabricated and measured, showing a good agreement between measurements and simulations, which demonstrates the validity of the proposed design approach.This work was supported by the Ministerio de Economía y Competitividad, Spanish Government, under the Research Project TEC2013-47037-C5-4-R

Design and Fabrication of a Band-Pass Filter With EBG Single-Ridge Waveguide Using Additive Manufacturing Techniques

A novel band-pass filter topology in waveguide technology is presented in this work. The proposed filter design is based on a periodic structure that uses modified sections of a single-ridge waveguide (SRW) as the unit cell to produce the desired frequency response. Two-step height profiles are included in the central part of the SRW, which provide useful parameters to yield a simple design method to achieve the required filtering characteristics. The suggested topology and design process are used to achieve band-pass filter responses with different fractional bandwidth and rejection characteristics. A 54% fractional bandwidth band-pass filter centered at 5.4 GHz is implemented using low cost 3-D additive manufacturing techniques, which allow fast prototyping and the fabrication of complex geometries. Experimental measurements are in agreement with the expected simulated response of the designed band-pass filter

UWB-Printed Rectangular-Based Monopole Antenna for Biological Tissue Analysis

This paper presents the design of a printed step-type monopole antenna for biological tissue analysis and medical imaging applications in the microwave frequency range. The design starts from a very simple and widely known rectangular monopole antenna, and different modifications to the antenna geometry are made in order to increase the bandwidth. The antenna dimensions are optimized by means of a parametric analysis of each dimension using a 3-D electromagnetic simulator based on the finite element method. The optimized antenna, with final dimensions of 40 36 mm2, is manufactured onto a low-cost FR4 (fiber glass epoxy) substrate. The characteristics of the antenna have been measured inside an anechoic chamber, obtaining an omnidirectional radiation pattern and a working frequency range between 2.7 GHz and 11.4 GHz, which covers the UWB frequencies and enables the use of the antenna in medical imaging applications. Finally, the behaviour of four of these antennas located around a realistic breast model, made with biocompatible materials, has been analysed with the electromagnetic simulator, obtaining good results and demonstrating the usefulness of the designed antenna in the proposed application