Full-wave characterization of bi-dimensional cavities and its application to the design of waveguide filters and multiplexers

[EN] Modern communications systems impose stringent requirements on the equipment that operates at microwave frequency, especially in the case of wireless communications. The design of passive components for these applications is contingent upon the availability of accurate electromagnetic (EM) modeling tools that can efficiently handle the complex geometry of these components. Despite the widespread use of mesh-based general-purpose computer-aided engineering (CAE) tools to perform final design verifications, their application during the optimization process is limited. Optimum designs require a large number of simulations, which are computationally expensive when performed by general purpose tools. Instead, microwave designers prefer to employ faster software tools tailored to specific geometries, such as waveguide components, multilayered structures, etc. Therefore, the development of faster and more efficient specialized EM tools has a direct impact on the design of microwave components, both quantitatively and qualitatively. Increasingly complex geometries are modeled more accurately, and may be incorporated into novel designs without penalizing development time and its associated costs. By doing so, passive components become more advanced and are able to fulfill stricter requirements. At the same time, new research and development opportunities arise in order to address the challenges posed by these advanced structures. The present thesis is focused on a specific type of waveguide cavity geometry: bi-dimensional structures of arbitrary shape. Most microwave components based on rectangular waveguides include these elements (bends, T-junctions, tapers, power-dividers, etc.), thus the scope of this work is wide. To characterize these structures, an efficient full-wave modal formulation is developed. Taking into account common properties of bi-dimensional structures, such as its electromagnetic symmetry, the resulting technique is very efficient and accurate. Thanks to the integration of this formulation into a CAE tool, a designer is able to solve complex systems that combine this type of element with components of vastly different shapes. The developed formulation is first applied to the analysis and design of passive components, such as filters, multiplexers and orthomode transducers. These examples are employed to validate the results, as well as to demonstrate the improvement that the proposed analysis technique represents over well-known commercial EM packages. Likewise, this formulation is combined with the tool SPARK3D to predict RF breakdown (multipactor and corona) in selected bi-dimensional structures. Then, novel implementations of waveguide quasi-elliptic filters, based on the interconnection of bi-dimensional cavities, are proposed. Special attention is paid to the realization of multiple transmission zeros (TZs) with tuning-less compact structures. First, a novel family of filters, known as hybrid-folded rectangular waveguide structures, is studied. Simple and flexible methods to prescribe the location of the transmission zeros realized by these structures are presented. Practical aspects related to their physical implementation are also discussed. Secondly, a compact and purely capacitive obstacle, capable of realizing multiple TZs, is presented and discussed. In both cases, multiple examples are given to illustrate the step-by-step process involved in the design of these structures. Finally, a systematic procedure for the design of wideband manifold-coupled multiplexers is proposed. To preven the generation of undesired resonances, stubs that connect the filters to the manifold are removed. Likewise, the manifold length is kept as short as possible. Following a simple procedure, based on analytical formulas and EM simulations, a good starting point for the final optimization of these structures is obtained. It has been applied to a wideband quadruplexer for passive intermodulation measurement at C-band.[ES] Actualmente, los sistemas de comunicaciones imponen unos requisitos muy estrictos sobre el equipamiento en la banda de microondas. El diseño de estos componentes está supeditado, frecuentemente, a la disponibilidad de herramientas de modelado electromagnético (EM) que sean capaces de analizar geometrías complejas. A pesar del amplio uso de herramientas CAE (computer-aided engineering) de propósito general para la verificación final de prototipos, su potencial aplicación durante el proceso de diseño es limitada. Los diseños óptimos exigen realizar una gran cantidad de simulaciones EM. Dado que las simulaciones con estas técnicas tienen un alto coste computacional, los diseñadores suelen optar por emplear herramientas software especializadas en las estructuras que diseñan. Por tanto, el desarrollo de nuevas herramientas más precisas y eficientes ayudará a reducir el tiempo de diseño de estos productos, y con ello los costes asociados. Además, permitirá abrir nuevas líneas de investigación para responder a los retos que plantean geometrías cada vez más complejas. Esta tesis se centra en el desarrollo de una herramienta de análisis EM para un tipo concreto de estructuras: cavidades bidimensionales de sección arbitraria. Es habitual encontrar este tipo de estructuras en la mayoría de componentes implementados en guía rectangular. Por tanto, el rango de aplicación de la teoría desarrollada en esta tesis es muy amplio. En concreto, se ha desarrollado una nueva formulación basada en métodos modales que permite realizar una caracterización de onda completa de estas estructuras de forma eficiente y precisa. Al aprovechar su simetría geométrica y electromagnética, la herramienta desarrollada puede minimizar los cálculos a realizar, consiguiendo grandes velocidades de computación pero manteniendo una alta precisión. Gracias a la integración de esta formulación dentro de una herramienta CAE basada en métodos modales, se ofrece la posibilidad a los diseñadores de resolver sistemas muy complejos que combinan este tipo de cavidades con otros componentes de geometrías distintas. Esta formulación se aplica, en primer lugar, al análisis y diseño de componentes pasivos comunes, tales como filtros, multiplexores y OMTs. Estos ejemplo validan la herramienta desarrollada, y demuestran la significativa mejora que supone el uso de esta nueva técnica con respecto a otros paquetes software de análisis electromagnético. Asimismo, al combinar esta formulación con la herramienta SPARK3D se abre la posibilidad de predecir la aparición de fenómenos de descarga de alta potencia en determinadas estructuras bidimensionales. A continuación, se proponen nuevas formas de implementar filtros cuasi-elípticos basados en la interconexión de cavidades bi-dimensionales. Se hace especial hincapié en la realización de múltiples ceros de transmisión mediante estructuras compactas que no requieran sintonía. Por una parte se estudian los filtros hybrid-folded rectangular waveguide. Este trabajo incluye una discusión en profundidad sobre distintas implementaciones de este tipo de filtros. En ella se consideran aspectos prácticos relacionados con su uso e implementación física, que ofrecen al diseñador unos criterios claros para elegir la estructura que más se ajuste a sus especificaciones. Por otra parte se presenta un nuevo obstáculo de naturaleza capacitiva muy compacto, que permite la realización de múltiples ceros de transmisión incluso en estructuras en línea. En ambos casos se incluyen ejemplos de aplicación y se describe la metodología seguida para su diseño. Finalmente, se expone un procedimiento sistemático para diseñar multiplexores de banda ancha. Para prevenir la generación de resonancias indeseadas se evitan, en la medida de lo posible, las interconexiones mediante tramos cortos de guía. Siguiendo una metodología simple se consigue un excelente punto inicial para su optimización. La te[CA] Els actuals sistemes de comunicacions sense fils imposen uns requisits molt estrictes sobre l'equipament de la banda de microones. El disseny d'aquests components està supeditat, frequentment, a la disponibilitat de ferramentes de modelatge electromagèntic (EM) que siguen capaços de gestionar geometries complexes. Tot i l'ampli ús de ferramentes CAE (computer-aided engineering) de propòsit general per a la verificació final de prototips, la seua aplicació durant el procés de disseny és limitada. Els dissenys òptims exigeixen realitzar una gran quantitat de simulacions. Les simulacions amb aquestes tècniques tenen un alt cost computacional, per tant els dissenyadors solen optar per utilitzar ferramentes software especialitzades en les estructures que dissenyen. Per tant, el desenvolupament de noves tècniques d'anàlisi més precises i eficients ajudarà a reduir el temps de desenvolupament d'aquests productes, i dels seus costos associats. A més permetrà obrir noves línies d'investigació per respondre els reptes que plantegen geometries cada vegada més complexes. Aquesta tesi es centra en el desenvolupament d'una ferramenta d'anàlisi EM per a un tipus concret d'estructures: cavitats bidimensionals de forma arbitraria. És habitual trobar aquestes estructures en la majoria de components implementats en guia rectangular. Per tant, l'àmbit d'aplicació de la teoria presentada en esta tesi és molt ampli. En concret, s'ha desenvolupat una nova formulació basada en mètodes modals que permet realitzar una caracterització d'ona completa d'aquestes estructures de forma eficient i precisa. Aprofitant la seua simetria geomètrica i electromagnètica, la ferramenta desenvolupada pot minimitzar els càlculs a realitzar, aconseguint grans velocitats de càlcul mantenint una alta precisió. Gràcies a la integració d'aquesta formulació dins d'una ferramenta CAE basada en mètodes modals, s'ofereix la possibilitat als dissenyadors de resoldre sistemes molt complexos que combinen aquest tipus de cavitats amb altres components de diferent geometria. Aquesta formulació s'aplica, en primer lloc, a l'anàlisi i disseny de components passius comuns: filtres, multiplexors i OMTs. Aquests exemples serveixen per a validar la ferramenta desenvolupada, així com demostrar la significativa millora que suposa l'ús d'aquesta nova tècnica respecte d'altres paquets software d'anàlisi electromagnètic. Així mateix, mitjançant la combinació d'aquesta formulació amb la ferramenta SPARK3D s'obri la possibilitat de predir l'aparició de fenòmens de descàrrega d'alta potència en estructures bidimensionals. A continuació, es proposen noves formes d'implementar filtres quasi el-líptics en guia d'ona basats en la interconnexió de cavitats bidimensionals. Es fa especial èmfasi en la realització de múltiples zeros de transmissió mitjançant estructures compactes que no requereixen de sintonia. D'una banda s'estudien els filtres hybrid folded rectangular waveguide. Aquest treball inclou una discussió en profunditat sobre diferents implementacions d'aquest tipus de filtres. S'hi consideren aspectes pràctics relacionats amb el seu ús i implementació física, que ofereixen al dissenyador uns criteris clars per triar l'estructura que més s'ajuste a les seues especificacions. D'altra banda es presenta un nou obstacle de naturalesa capacitiva extremadament compacte, que permet la realització de múltiples zeros de transmissió fins i tot en estructures en línia. En els dos casos s'inclouen exemples d'aplicació i es descriu la metodologia seguida per al seu disseny. Finalment, s'exposa un procediment sistemàtic per dissenyar multiplexors de banda ampla. Per prevenir la generació de ressonàncies no desitjades s'eviten les interconnexions amb trams de guia curts. Seguint una metodologia simple, basada en fórmules analítiques i simulacions electromagnètiques, s'aconsegueix un excel-lent punt inicial per a l'optimització.Carceller Candau, C. (2016). Full-wave characterization of bi-dimensional cavities and its application to the design of waveguide filters and multiplexers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/64089TESI

Design and Analysis of the Medium-β Elliptical Cavities for the European Spallation Source Accelerator

This thesis is dedicated to the design and analysis of superconductingelliptical cavities. Elliptical cavities play a central role in modern particle ac-celerators due to their high efficiency. After an introduction to the EuropeanSpallation Source project, the thesis goes through the design of the medium-βcavity. The RF design of the inner cell and end cell are presented in sequencein paper I . The design is completed by the chapter on the mechanical perfor-mances of the cavity (paper II).Papers III, IV and V are instead dedicated to the analysis of the cavity.The necessary mathematical tools for the analysis are presented in paper IIIwhich, after stating fundamental results on hollow cavities, presents a spec-tral decomposition used in the following papers. In paper IV, a time-domainmodel for the power dissipation induced by the excited higher-order-modes ispresented. Such modes are excited by the particle beam that passes throughthe cavity and are detrimental to the performances of the accelerator. PaperV presents a time-domain model of the cavity coupled to an externa circuit toa coupler. The model is functional to the design of the cavity control system

Full-wave analysis and design of passive microwave and millimetre-wave devices based on dielectric-loaded cavity resonators

Desde los primeros estudios desarrollados por S.B. Cohn a finales de los años 60, los resonadores dieléctricos, con factor de calidad elevado, han sido utilizados para el diseño de filtros paso-banda de microondas. A partir de la aparición en los años 70 de materiales dieléctricos con las propiedades eléctricas y estabilidad térmica idónes, los resonadores dieléctricos se convirtieron en elementos clave en numerosos diseños de filtros. De hecho, esta tecnología se encuentra frecuentemente en sistemas de comunicaciones míviles y por satélite debido a sus ventajas en términos de reducción de masa y volumen, bajas pérdidas, y estabilidad térmica. Por todo ello, el análisis y diseño riguroso de este tipo de filtros ha suscitado un gran interés en la literatura técnica. El objetivo principal de esta tesis doctoral es el desarrollo de una técnica modal eficiente para caracterizar el comportamiento electromagnético de cavidades resonantes cargadas con dieléctricos. Para ello, se presenta una nueva formulación de ecuación integral en el espacio de estados basada en el método BI-RME (del inglés, boundary integral-resonant mode expansion). En dicha formulación, para resolver la ecuación integral de volumen planteada, el resonador dieléctrico se caracteriza de manera rigurosa por medio de las densidades de carga y corriente de polarización equivalentes definidas en el volumen del objeto dieléctrico. Siguiendo este método, los modos resonantes de las cavidades se obtienen a través de la solución de un problema lineal de autovalres. Así mismo, se obtiene la matriz generalizada de admitancias de la cavidad resonante cargada con dieléctrico como una expansión en serie de polos en el dominio de la varable de Laplace. De esta manera, la respuesta electromagnética de las cavidades resonantes puede resolverse en un rango amplio de puntos de frecuencia haciendo uso de un reducido esfuerzo computacional, y evitando así, cálculos intensos en cada punto de frecuencia.Gil Raga, J. (2010). Full-wave analysis and design of passive microwave and millimetre-wave devices based on dielectric-loaded cavity resonators [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/7442Palanci

Multidimensional Compressible Framework for Modeling Biglobal Stability in Rocket Motors

Rocket motor stability analysis has historically been focused on two fundamental theories: the acoustic and the hydrodynamic. While the acoustic part examines the system at resonant states, the hydrodynamic component focuses on the fluid-wall interactions and the vortex shedding mechanisms which are responsible for exciting the system. Traditionally, the two concepts are studied independently and their results are then superposed for a more complete solution. In this study, we analyze the problem from a hydrodynamic standpoint and extend it to include compressibility. This is realized by reducing the linearized Navier-Stokes and energy equations to their biglobal form assuming a two-dimensional waveform with a sinusoidal temporal dependence. The suggested approach is found to be comprehensive, capturing both hydrodynamic and acoustic fields simultaneously. Doing so unifies the two phenomena commonly associated with combustion instability while accounting for interactions between resonant and non-resonant eigenmodes. In this work, results are compared and validated using analytical solutions of the vortico-acoustic waves, which incorporate a viscous correction at the wall. Regarding the hydrodynamic component, comparisons to numerical results verify the captured modes. Combined, they present an improved agreement with experimental data for the cold air injection setup. By retaining the influence of the mean flow on the unsteady motion, the technique straightforwardly displays a slight frequency shift from the Helmholtz type acoustic modes, thus confirming the behavior observed in numerous experiments. Moreover, the modal analysis extends over both the longitudinal and transverse modes, thus providing the full spectrum of the system modes related to both acoustics and hydrodynamics. In short, the present work provides physical insight into hydrodynamic-acoustic interactions leading to vortex synchronization and frequency shifting that may be associated with the amplified frequencies captured in live rocket firings. The framework presented here may be viewed as a substantial advancement in the field of biglobal stability, namely, in its ability to capture the full effects of compressibility and shearing simultaneously

Laser produced electromagnetic pulses : Generation, detection and mitigation

This paper provides an up-to-date review of the problems related to the generation, detection and mitigation of strong electromagnetic pulses created in the interaction of high-power, high-energy laser pulses with different types of solid targets. It includes new experimental data obtained independently at several international laboratories. The mechanisms of electromagnetic field generation are analyzed and considered as a function of the intensity and the spectral range of emissions they produce. The major emphasis is put on the gHz frequency domain, which is the most damaging for electronics and may have important applications. The physics of electromagnetic emissions in other spectral domains, in particular THz and MHz, is also discussed. The theoretical models and numerical simulations are compared with the results of experimental measurements, with special attention to the methodology of measurements and complementary diagnostics. Understanding the underlying physical processes is the basis for developing techniques to mitigate the electromagnetic threat and to harness electromagnetic emissions, which may have promising applications

Polaritonics : an intermediate regime between electronics and photonics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.Includes bibliographical references (p. 279-290).This thesis contains the foundational work behind the field of polaritonics. Corresponding to a frequency range from roughly 100 gigahertz up to 10 terahertz, polaritonics bridges the gap between electronics and photonics. In this regime, signals are carried by an admixture of electromagnetic and lattice vibrational waves known as phonon-polaritons, rather than currents or photons. Impulsive stimulated Raman scattering (ISRS) is employed for phonon-polariton generation, whereby lattice vibrations are driven by optical femtosecond laser pulses directed into ferroelectric LiNbO3 or LiTaO3. The vibrational amplitude is proportional to the intensity of the excitation pulses. Due to the high dielectric constants of these crystals, phonon-polaritons travel in a predominantly lateral direction away from the excitation region. Lateral propagation is further facilitated by employing crystals whose thickness is on the order of the phonon-polariton wavelength, such that propagation occurs within one or more of the slab waveguide modes of the crystal. Direct observation of phonon-polaritons is achieved using real-space imaging, which monitors and records the spatiotemporal evolution of phonon-polaritons within a ferroelectric crystal. The details of both broadband and narrowband phonon-polariton generation and propagation in bulk and thin film crystals are presented. Additionally, robust polaritonic waveform generation is illustrated that relies on temporal or spatial shaping of the optical excitation pulses. Guidance, control, and other types of signal processing are demonstrated by patterning of the host crystal using femtosecond laser micromachining.(cont.) Waveguides that direct propagation, resonators that confine polaritonic signals, reflectors that direct, shape, and focus polaritonic waveforms, and periodic photonic crystal structures that restrict phonon-polaritons to a narrow band of frequencies are fabricated and their functionality demonstrated. The details of the laser micromachining employed for fabrication of these structures in a variety of crystal thicknesses are also presented here. Experimental measurements are supported by a novel implementation of finite-difference- time-domain (FDTD) simulations that accurately model both phonon-polariton generation and propagation in bulk, thin film, and patterned crystals. Additionally, numerical experiments are performed to predict functionality that will enable advanced polaritonic bistable devices for use in digital polaritonics and negative refractive polaritonic materials for unique waveform generation, signal processing, and sub-diffraction terahertz imaging. Polaritonics offers lower signal-to-noise than photonics and higher bandwidth signals than electronics, with generation, propagation, guidance, and control integrated into a single all- optical platform. Direct visualization of signal propagation makes device design and testing substantially easier than in either electronics or photonics. With continued development, fabrication of polaritonic materials should prove less demanding than traditional photonic structures, as it requires feature sizes on the order of micrometers rather than nanometers. Due to the high terahertz electric field strengths associated with ISRS phonon-polariton generation and the robust signal processing tool chest presented here, polaritonics promises to be useful in various spectroscopic applications including, but not limited to, linear and nonlinear terahertz spectroscopy and terahertz near field microscopy.by David W. Ward.Ph.D

Compact State-Space Models for Complex Superconducting Radio-Frequency Structures Based on Model Order Reduction and Concatenation Methods

The modeling of large chains of superconducting cavities with couplers is a challenging task in computational electrical engeneering. The RF properties of the arising segments are described by state-space equations. Their model order is reduced and the reduced-order models are concatenated in accordance with the topology of the complete structure. The scheme enables the investigation of radio-frequency properties of large structures without the application of supercomputers