Electromagnetic Modelling of Planar Circuits Embedded in Laterally Shielded Multilayered Media

Laleh Golestanirad
EPFL, 2011
Thèse EPFL

Résumé

Multilayered media with printed circuits embedded between their dielectric layers are one of the most successful technologies for manufacturing planar structures with a very promising performance-to-price ratio. These planar structures include many different geometries ranging from cavity-backed microstrip antennas through Frequency Selective Surfaces (FSS) and photonic band-gap structures, to shielded printed circuits and ultra-wide-band slot-line microwave filters. The electromagnetic characteristics of such structures can be modeled with a wide range of numerical techniques. In recent years we have witnessed a remarkable progress in developing numerical solvers specialized in analyzing specific electromagnetic problems including the Integral Equation technique (IE) solved by the Method of Moments (MoM) which has proven to be very robust and efficient in the framework of partially open or shielded planar structures. As a part of this study an efficient CAD tool was developed based on the IE formulation and implemented in the context of the MoM technique. It includes a rigorous mathematical formulation of the electromagnetic problem which automatically incorporates the effects of the metallic shield (cavity) and the multilayered substrate which supports different layers of metallization (interfaces). A comprehensive study has been carried out to point out the convergence of the proposed algorithm along with a detailed validation, verification and benchmarking plan. The tool is developed in such a way that is capable of working with a hybrid mesh (combination of both rectangular and triangular cells) which gives it a great flexibility in analyzing any arbitrarily-shaped embedded circuitry. To enhance the overall performance of the algorithm, symmetry options have been formulated and implemented. These additional features have shown to dramatically reduce the computational and temporal requirements and thus expand the range of microwave devices which can be efficiently analyzed by the software, such as filters based on waveguide structures and FSSs. Other enhancement techniques have been envisaged based on selective MoM matrix member calculation which successfully reduce the number of unknowns in large microstrip layouts while maintaining an acceptable accuracy. Mathematical formulations are developed to provide the capability of handling lumped ports (representing coaxial-line feeds) and waveguide excitations. The implementation of combined ports in the framework of planar multilayered structures is shown to be practically useful in analyzing systems that have both waveguide connections and planar circuitries in their structure as it enables the application of highly specialized algorithms in the analysis of each part of the system and subsequent communication of the network characterizations at the ports' interfaces. This approach has considerably enhanced the overall performance of the analysis tool by reducing the computation time and memory requirements to a great extent.

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https://infoscience.epfl.ch/record/162119?ln=fr

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Laleh Golestanirad
EPFL, 2011
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/162119?ln=fr

À propos de ce résultat

Concepts associés (25)

Concepts associés

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Publications associées (28)

Publications associées

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3D analysis and optimization of microwave circuits by the method of moments

Francisco Jesus Nunez

The design and minaturization of microwave circuits involves the analysis and optimization of a large varity of structures, which, in general, are based on arbritrary objects embedded in also arbritary media. The most common situation is found when optimizing terminal antennas, whose main constraint is the antenna's volume, which must be fitted into a specified space, which in general is the phone or laptop case. This kind of antennas can also include stratified media, oblique metallizations, dielectric objects, waveguide components, in their definition making their analysis more difficult from the numeric point of view. The complete treatment of this kind of problems has been performed traditionally using Finite Differences or Finite Elements software, while it is more rare to find Method of Moments implementations for the solution of this kind of general problems. The Method of Moments has a certain number of advantages as the inclusion of radiation conditions or stratified media in the Green's function of the problem. Due to this it is possible to mesh only the surfaces or boundary conditions that are not included in the Green's function definition, obtaining, for instance, a more natural radiation boundary condition compared to other fullwave methods. The other big concern is the optimization of this kind of structures. In general the structures we are dealing with in this work can have very irregular shapes, in order to fit within the required volume constraints. The traditional optimizations techniques based on the gradient or conjugated gradient are not efficient when optimizing functions containning multiple minima and a large search space, which is the case in the optimization of terminal antennas. When miniaturizing terminal antennas or just a simple microstrip filter, the number of unknowns can be very large, and the different optimization variables can vary within wide limits in the search space. In this situation the Genetic Algorithms are ideal for seeking the global optimum solution of our problem. This work covers the analysis and optimization of microwave circuits, including antennas and filters in microstrip and waveguide technologies, paying more attention to the implementation of the Method of Moments (MoM) in conjugation with the Mixed Potential Integral Equation (MPIE) and Electric/Magnetic Field Integral Equation (EFIE/MFIE). The work has been split into 3 main goals: The analysis of 3 dimensional structures in stratified media, including arbritary shaped dielectric bodies using the Method of Moments, (MPIE,EFIE,MFIE). The analysis of shielded environments and more precisely the analysis of retangular waveguide cavities with the Method of Moments. The implementation of several optimization techniques, emcompassed in the frame of genetic algorithms, for the design and miniaturization of terminal antennas and microstrip filters. Some relevant examples linked to the efficiency and accuracy of the different methods and techiques explained in this work are included in each chapter, yielding to practical results suitable to be used in real life design problems. The main contributions of this work can be summarized as follows: In Chapter 2 we have developed the interpolation of 3D Green's function to the general solution of dielectric objects embedded in multilayered media. The interpolation method itself is preceeded by a spectral extraction of the quasi-static terms. This technique, very often applied in complex images techniques, has been applied to our specific Green's function problem yielding very good results in terms of accuracy and Green's function computation time. Another contribution, also emcompassed in Chapter 2, is the integration of the static part of the field dyadic G̿EM, performed by splitting the field dyadic into TM and TE components, allowing then an analytical integration of the dyadic terms in stratified media. In the frame of shielded environments in Chapter 3, the most important contribution is the extension of Ewald's acceleration technique to full electric and magnetic problems, allowing the acceleration of the field dyadic G̿EM and thus permit the extension of the MoM to the simulation of arbritary metallic shapes coupled to apertures through Ewald's approach. In Chapter 4 the most important contribution is the implementation of a Bayesian optimiser based on the estimation of probability made by dependencies trees. The dependency tree based method found in [1] and later in [2] has been adapted to the terminal antenna miniaturization yielding to excellent results in optimisation time and quality of the solution provided by the optimiser. Our implementation of the dependency tree method was found to be better than the traditional method used in this kind of problems. Chapter 4 contains also an implementation of the growing cells method presented in [3] for the specific problem of optimising pseudo periodic structures, like microwave filters, yielding to a powerful interpolating method which accelerates the optimisation process of microwaves devices whose fitness response is very time consuming.

EPFL2006

Chargement

Electromagnetic Simulation of CERN Accelerator Components and Experimental Applications

Carlo Zannini

Wakes and impedances of single accelerator elements can be obtained by means of theoretical calculation, electromagnetic (EM) simulations or bench measurements. Since theoretical calculations apply only to simple structures and bench measurements have some intrinsic limitations, EM simulations can be used as a reliable tool to determine wakes and impedances. This thesis will focus on the use of time domain 3D CST Particle Studio EM simulations to calculate wakes and/or impedances. First, the results of the EM simulations are compared with the known analytical solutions and other codes. In this exercise, the driving and the detuning terms of the wakes/impedances, in the transverse plane, are disentangled for both symmetric and asymmetric geometries. The sensitivity of the simulations results to the numerical parameters is discussed, as well as the limits of validity of the wake formalism and its extension to the nonlinear regime. Using the CST Wakefield Solver, the SPS kicker impedance contribution is then estimated. The simulation model was improved step by step, and successfully benchmarked with existing and new theoretical models, giving confidence in the numerical results and allowing a better understanding of the EM problems. In the case of the resistive wall impedance of simple chamber geometries a handy theoretical model has been proposed. In order to calculate the resistive wall impedance of a round chamber, a theoretical approach based on the transmission line (TL) theory, is demonstrated to be valid and practical to use. By means of appropriate form factors the method is then extended to rectangular or elliptical chambers. Moreover the method was successfully benchmarked with the most recent codes based on the field matching technique developed at CERN and was used to construct the SPS wall impedance model. For more complicated geometries (asymmetries, small inserts, holes etc.), a theoretical estimation without involving EM simulation becomes unworkable. An example of interest is the LHC beam-screen, for which CST 3D simulations were used to estimate the impedance. In order to allow the simulator to cover the whole frequency range of interest (few KHz to several tens of MHz) a novel scaling technique was developed and applied. Where possible, the EM models developed throughout this thesis were also successfully benchmarked with bench measurements (wire methods) and observations with beam. On the specific subject of bench measurements, a numerical investigation of coaxial wire measurements has been also presented. Finally, in order to verify the adopted EM models of the materials both in theoretical calculations and 3D simulations, an experimental setup for measuring EM properties (permittivity and permeability) of materials has been presented. The method is based on fitting the measured reflection transmission coefficients through a coaxial line filled with the material to be probed, with the outcome of EM simulations or theoretical models. It was successfully applied for measuring NiZn ferrites and dielectric material (e.g. SiC).

EPFL2013

Chargement

Printed circuits in bounded media encompass a wide range of practical structures such as discontinuities in waveguides, planar circuits embedded in shielded multilayered media or even two-dimensional printed periodic structures. The Electromagnetic (EM) modeling of printed circuits in layered bounded media is performed via an Integral Equation (IE) technique. Green's functions (GFs) are specially defined to satisfy both the Boundary Conditions (BCs) imposed by the layered media and by the transverse boundary enclosing the entire structure. Finally, a system of IEs on the equivalent sources can be solved numerically by means of the Method of Moments (MoM). Each of the problems enumerated above has already been solved by other authors using IE-MoM techniques. Nevertheless, our formulation introduces a unified approach applicable to all the aforementioned problems. Due to the symmetry presented by a bounded layered media, the GF problem can be reduced into a two-dimensional transverse boundary problem and a one-dimensional transmission line problem in the normal direction. Both problems can be treated independently. This thesis proposes and fully develops an efficient technique that encompasses different laterally bounded multilayered problems with a seamless transition between them. The method is based on a modal representation of the transverse boundary problem and on the expansion of the equivalent surface currents by zero-curl & constant-charge Basis Functions (BFs). It offers a unified and versatile approach that, on one hand eliminates redundancy in the formulation and on the other hand simplifies each particular problem to the evaluation of constant coefficients or basic line integrals. Analytical solutions can be found for the combination of linear subsectional basis functions in rectangular and circular Perfect Electric Conductor (PEC) boundaries as well as for periodic lattices. This thesis then solves the problem of transmission line model in the longitudinal direction by proposing an efficient algorithm that guarantees numerical stability under a variety of known critical conditions where other already known formulations fail. In addition, it introduces alternate equivalent expressions of this formulation that allow new interpretations of the problem. Due to its practical interest, the method is applied for the EM modeling of multilayered boxed printed circuits. This motivated the implementation of a dedicated software tool for the efficient analysis of these topologies including losses. Extensive numerical experiments have been carried out to assess the validity of the aforementioned theory and some properties of test-structures (losses, mesh, etc).

EPFL2007

Chargement

3D analysis and optimization of microwave circuits by the method of moments

Francisco Jesus Nunez

EPFL2006

Electromagnetic Simulation of CERN Accelerator Components and Experimental Applications

Carlo Zannini

EPFL2013

EPFL2007