Because the metal enclosure with apertures is the structure of the cavity form, FDTD method belonging to full-wave analytical algorithm isn¡¦t efficient for analyzing such case. Thereby the ETL method belonging to analytical formulation provides another way to analyze it. Although the structure which it can apply to isn¡¦t as complex as that in full-wave analytical algorithm, the computing time is shorter than FDTD. In contrast, the method can¡¦t get good agreement. Thus two improved ways are introduced in this paper. One is to make the suitable structure wider and the other is to consider the higher mode original ETL method isn¡¦t included to improve the accuracy. Further these two ways make the suitable range of the method wider and the method has good practicability.

The finite-difference time-domain (FDTD) method is one of the most popular numerical electromagnetic analysis tools. This method has been applied to a wide variety of problems such as antennas, electronic packaging, waveguides, etc. However, it is not suitable for large scale structures. The enormous memory requirement prohibits the use of FDTD to a large electrical size. Recently, the pseudospectral time-domain (PSTD) method has been introduced for solution of Maxwell¡¦s equation. This method adopts the Fourier transform algorithm to perform the spatial derivatives. According to Nyquist sampling theorem, it requires only 2 cells per wavelength, so that it is possible to efficiently model larger scale problems. This thesis describes a combination of PSTD and FDTD method applied in different directions. The FDTD be applied to directions along fine structures and the PSTD be applied in direction along large structures.

FDTD is a numerical method that uses the second-order central-difference method to discrete the Maxwell¡¦s equations in differential form, and positioning electromagnetic field in space grids and time grids. It is applied to analyze many electromagnetic problems in time domain. In this report the FDTD method is extended to include lumped-elements (as resistor, inductor, capacity),and nonlinear elements(as diode, transistor) to combine the circuit elements and electromagnetic fields, it¡¦s so called LE-FDTD algorithm. The first, we will introduce the theory derivations and simulate some circuit structures in 2D, and then in order to simulate the real circuits, we will extend this algorithm in 3D to make full-wave analysis.

FDTD is an electromagnetic field computation method with the ability of considering circuit elements. Traditional lump element method is insufficient for simulating circuit. In this thesis, we use equivalent source method to combine non-linear circuit elements like active devices into the FDTD simulation. The advantages of this is powerful and time-saving. The accuracy of this method is checked of transmission line driving by CMOS circuits. By employing this method, we find that it will increase EMI phenomenon by strengthening current of driving load, and the load of coupling line will affect noise due to impedance mismatch.

In recent years, the demand for portable radio communication has been increasing which requires low profile, light weight and small size antennas. Therefore, the size of the antenna is required to be as small as possible. In this thesis, some of the compact antennas will be analyzed and simulated. The early-stage PIFA antenna will be investigated first, and then the shorting pin characteristics to design compact and dual band antenna was utilized. Because the shorting pin will lead to the decrease of bandwidth, replacement of the shorting pin by using chip-resistor could improve this characteristic. The compactness of antennas will lead to the decrease of the gain. In order to improve the gain of antennas, the combination of substrate and superstrate configuration with very high permittivity material is used. For the consideration of Bluetooth system, we use the ACPS (Asymmetrical Co-planar Striplines) structure to design the antenna. Using this structure in the design will obtain a promotion in bandwidth compared with the conventional rectangular microstrip antenna. Because the size of the antenna is small, the time to simulate this structure by the FDTD (Finite Difference Time Domain) method is too long. In order to solve this problem, this thesis mainly study a new FDTD algorithm based on the Alternating-Direction Implicit method, and use this algorithm to simulate some simple structures.

This thesis is made up of three parts on the computation of scattering properties of nonspherical particles in the atmosphere. In the first part, a new crystal type-droxtal-is introduced to make a better representation of the shape of small ice crystals in the uppermost portions of midlatitude and tropical cirrus clouds. Scattering properties of droxtal ice crystals are investigated by using the Improved-Geometric Optic (IGO) method. At the visible wavelength, due to the presence of the hexagonal structure, all elements of the phase matrix of droxtal ice crystals share some common features with hexagonal ice crystals, such as 220 and 460 halos. In the second part of this thesis, the possibility of enhancing the performance of current Anomalous Diffraction Theory (ADT) is investigated. In conventional ADT models, integrations are usually carried out in the domain of the particle projection. By transforming the integration domain to the domain of scaled projectile length, the algorithm of conventional ADT models is enhanced. Because the distribution of scaled projectile length is independent of the particle's physical size as long as the shape remains the same, the new algorithm is especially efficient for the calculation of a large number of particles with the same shape but different sizes. Finally, in the third part, the backscattering properties of nonspherical ice crystals at the 94GHz frequency are studied by employing the Finite-Difference Time- Domain (FDTD) method. The most important factor that controls the backscattering cross section is found to be the ratio of the volume-equal radius to the maximum dimension of the ice crystal. Substantial differences in backscattering cross sections are found between horizontal orientated and randomly oriented ice crystals. An analytical formula is derived for the relationship between the ice water (IWC) content and the radar reflectivity ( e Z ). It is shown that a change to the concentration of ice crystals without any changes on the size distribution or particle habits leads only to a linear e Z IWC - relationship. The famous power law e Z IWC - relationship is the result of the shift of the peak of particle size distribution.

The finite-Difference Time Domain method (FDTD) derives the discrete form of the Maxwell¡¦s equations with second-order central difference with the electromagnetic distribution of the Yee space lattice, and computes the value of the electric field and magnetic field in the simulation space using leapfrog for time derivatives. This method is different from the frequency domain method which needs to analyze its value individually (ex. Finite Element method). The frequency domain method needs to take a long time for analyzing the response on each spectrum point when the bandwidth is very wide. The advantage of time domain analysis is to obtain the complete frequency response from the simulation value through Fourier Transform method. It¡¦s difficult to combine the electromagnetic analysis with the lumped circuit simulation in current simulation CAD. Thereby the performance of the simulation result and the practical implementation always causes error. The FDTD method is the full-wave algorithm which can also simulate the lump element, nonlinear element or active element in simulation space by linking to SPICE or S-parameter. In this dissertation, an efficient scheme for processing arbitrary one-port devices in the finite-difference time-domain (FDTD) method is proposed. Generally speaking, methods invoking analytic pre-processing of the device¡¦s V-I relations (admittance or impedance) are computationally more efficient than methods employing numerical procedure to iteratively process the device at each time step. The accuracy of the proposed method is verified by comparison with results from the equivalent current-source method and is numerically stable.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2007. / Submitted by Luis Felipe Souza (luis_felas@globo.com) on 2008-11-25T16:43:41Z No. of bitstreams: 1 Dissertacao_2007_CarlosEvangelistaJunior.pdf: 4060941 bytes, checksum: 0412bca1e07872e3de59fc9a31fc007d (MD5) / Approved for entry into archive by Georgia Fernandes(georgia@bce.unb.br) on 2009-02-09T11:43:11Z (GMT) No. of bitstreams: 1 Dissertacao_2007_CarlosEvangelistaJunior.pdf: 4060941 bytes, checksum: 0412bca1e07872e3de59fc9a31fc007d (MD5) / Made available in DSpace on 2009-02-09T11:43:11Z (GMT). No. of bitstreams: 1 Dissertacao_2007_CarlosEvangelistaJunior.pdf: 4060941 bytes, checksum: 0412bca1e07872e3de59fc9a31fc007d (MD5) / A crescente demanda por serviços de telecomunicações, sobretudo comunicações sem fio, e o congestionamento do espectro de radiofreqüências têm motivado o desenvolvimento de novos dispositivos de microondas com melhor desempenho e tamanho reduzido. Os ressoadores dual-mode são dispositivos com características altamente desejáveis dentro deste contexto, sobretudo por sua contribuição na redução de tamanho e peso. No presente trabalho, será estudada sua aplicabilidade na confecção de filtros. Inicialmente será realizado o modelamento do anel ressoador para a determinação de suas freqüências de ressonância. Em seguida, será feita uma análise comparativa das diferentes estratégias de alimentação desse ressoador. Por fim, serão estudados o modelamento e as topologias de estruturas com anéis ressoadores dual-mode e sua aplicação na construção de filtros. As simulações apresentadas ao longo deste trabalho foram realizadas por meio de um software que implementa o método das Diferenças Finitas no Domínio do Tempo (FDTD – Finite Difference Time Domain). Foi construído e medido um protótipo de filtro utilizando ressoadores dual-mode para consolidar o trabalho e validar o software na prática. ______________________________________________________________________________________ ABSTRACT / The increasing demand for telecommunications services and the congestion of the radio frequencies spectrum have motivated the development of new devices with performance improved and small dimensions. This work will focus on dual-mode ring resonators and its applicability on the issue of assembly of filters. Initially, the model of the ring resonator and its resonance frequencies has been studied. Afterwards, a comparative analysis of different strategies of feeding have been made. Finally it has been studied the modeling of the structures with dual-mode rings resonators and a filter with this topology have been assembled. The simulations of this dissertation had been made by a developed software which implements the Finite Difference Time Domain method (FDTD).

Les travaux de cette thèse ont été consacrés à l'extension du domaine d'application de la FDTD à Grille Double (DG-FDTD) via son hybridation avec l'Optique Physique Itérative. Ces recherches ont été motivées par le besoin d'évaluer précisément et efficacement le diagramme d'antenne environnées installées sur des plates-Formes de grandes dimensions (satellite, véhicule, lanceur spatial). Lors du tour d'horizon consacré aux méthodes numériques pouvant intervenir dans la résolution de ce type de problème, la DG-FDTD a révélé des caractéristiques intéressantes en permettant des analyses large bande rapides et précises d’antennes avec un environnement proche complexe. Cependant, sa formulation rigoureuse entraîne des besoins importants en ressources informatiques pour analyser des problèmes de grandes dimensions électriques. Les travaux présentés dans ce manuscrit précisent les limites de son domaine d'application. Ils mettent finalement en avant son incapacité à résoudre seule des problèmes d'antenne sur plateforme. En réponse à cette limitation, un nouveau schéma hybride associant la DG-FDTD avec une méthode asymptotique est proposé. La méthode DG-FDTD/IPO ainsi créée décompose la simulation du problème complet en deux simulations successives. L'antenne et son environnement proche sont tout d'abord simulés rigoureusement avec la DG-FDTD puis la plateforme est analysée efficacement avec l'IPO. Les deux simulations sont interfacées en utilisant le principe d’équivalence. Après avoir validé cette nouvelle méthode sur un scénario canonique, elle est appliquée au calcul de rayonnement électromagnétique en champ lointain dans deux scénarios d’antenne environnée sur porteur (antenne sur véhicule notamment). Deux améliorations de la DG-FDTD/IPO sont finalement proposées dans ce manuscrit. La première est consacrée à la prise en compte grossière des couplages retours entre l'environnement proche de l'antenne et la plate-Forme. Cette amélioration repose sur la redescription grossière de l’environnement proche de l’antenne dans la simulation IPO. La seconde amélioration concerne la modélisation des courants sur les parties ombrées de la plate-Forme dans la simulation IPO. Cette amélioration est motivée par le besoin d'analyser précisément des scénarios de type antenne sur lanceur spatial. En effet, l'IPO ne calcule pas les courants sur les zones ombrées, or dans ce type de problème elles représentent la majeure partie de la plate-Forme. Une nouvelle méthode basée sur l'IPO, et appelée Traitement Séquentielle des Domaines (TSD), est donc proposée pour répondre au besoin exprimé plus haut. Après avoir validé cette nouvelle méthode sur un cas simple impliquant un cylindre, elle est appliquée avec succès à l'analyse d'une plate-Forme de type lanceur spatial. / This thesis aims at extending the Dual-Grid FDTD (DG-FDTD) application domain via its hybridization with the Iterative Physical Optics (IPO) method. This research was motivated by the need to evaluate accurately and efficiently the antenna pattern of surrounded antennas installed on large platforms (satellite, vehicle, space launcher). Overview on numerical method involved in this class of problem revealed DG-FDTD has interesting features. This method allows precise and efficient wide-Band simulations of surrounded antennas. However, this method remains costly for electrically large problems, especially because of its rigorous formulation. This thesis assessed the limitations of DG-FDTD and then put forward its inability to resolve antenna on platform problems. To answer this issue, a hybrid scheme combining DG-FDTD with IPO is proposed in this thesis. DG-FDTD/IPO divides the initial simulation into two successive simulations. The antenna and its vicinity are firstly analyzed with DG-FDTD, and then IPO is used to analyze the platform. The two simulations are interfaced using the equivalence principle. This new method is first validated using a canonical scenario. Then, it is applied to the computation of electromagnetic radiation pattern in two antenna on platform problems (antenna on vehicle especially). The method is then exploited to effectively analyze the radiation pattern of a surrounded antenna mounted on a platform. Two improvements are finely proposed in this thesis for DGFDTD/ IPO. The first one aims at taking into account for the backward coupling between the antenna region and the metallic platform. This improvement implies a coarse description of the antenna region in the IPO simulation. The second improvement concerns the modeling of the currents in the shadow areas of the platform. This improvement answers to the need to analyze precisely antenna-On-Launcher problems. Indeed IPO do not compute currents in shadow areas. Well, for this kind of problem, shadow areas represent almost all the platform. A new method based on IPO and called Domains Sequential Processing is proposed. This method is first validated using a canonical scenario involving a cylinder. Then it is successfully applied to the analysis of a spatial launcher.

This thesis deals with problems of electromagnetic fields' simulations in the aerospace industry. Electromagnetic effects of the external environment that maybe met during a standard flight (high-intensity radiated fields and lightning strike) are described hereinafter with a reference to their simulations on a digital mockup. A brief summary of the nowadays methods and solvers in computational electromagnetics to be practically used for the modeling and simulations in this field is elaborated as a base for the following parts of the diploma task. The next goal was to create a convenient model simulation of the researched object semi-composite aircraft EV55, on which chosen computing methods will be compared with the results of the real measuring.