F. D. Quesada Pereira

Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions

[1] A technique for the accurate computation of the time domain electromagnetic fields radiated by a charged distribution traveling along an arbitrarily shaped waveguide region is presented. Based on the transformation (by means of the standard Fourier analysis) of the time-varying current density of the analyzed problem to the frequency domain, the resulting equivalent current is further convolved with the dyadic electric and magnetic Green’s functions. Moreover, we show that only the evaluation of the transverse magnetic modes of the structure is required for the calculation of fields radiated by particles traveling in the axial direction. Finally, frequency domain electric and magnetic fields are transformed back to the time domain, just obtaining the total fields radiated by the charged distribution. Furthermore, we present a method for the computation of the wakefields of arbitrary cross-section uniform waveguides from the resulting field expressions. Several examples of charged particles moving in the axial direction of such waveguides are included.

Analysis of finite microstrip structures using an efficient implementation of the integral equation technique

An efficient numerical implementation of the integral equation technique (IE) has been developed for the analysis of the electrical characteristics of finite microstrip structures. The technique formulates a volume version of the IE for the finite dielectric objects. The numerical implementation combines rooftop basis and testing functions for the conducting metallic areas, and two different choices for the dielectric objects. The first is based on a classical approach, combining pulse basis functions and deltas for testing. The second is a novel full Galerkin approach which employs rooftop functions defined on brick cells inside the dielectrics. The input impedances of two microstrip antennas have been computed with the new technique, showing good agreement with respect measurements. Also the radiation patterns of the antennas have been evaluated, showing again good agreement with respect to measurements. The practical value of the approach is that microstrip circuits can be designed minimizing the volume and size of the dielectric substrates. In addition, it is possible to accurately predict the backward radiation of practical microstrip radiators.

A novel technique for the analysis of complex antennas with rotational symmetry using a simple thick wire model

A simple technique based on the analysis of thick wire elements is applied to the characterization of complex antennas exhibiting rotational symmetry. Results show that the technique allows the accurate analysis of complex antennas, of thick radius above 0.1/spl lambda/, composed of cylindrical and conical elements. The value of the derived approach is that it can replace otherwise time consuming numerical techniques based on surface discretization, while achieving a similar degree of accuracy.

A novel approach for the evaluation of electromagnetic fields using rigorous wire antenna models

Wire antenna models are a useful approach for studying small cylindrical elements using Integral Equation (IE) formulations [1, 2, 3]. For an accurate application of these models in the Method of Moments (MoM), some techniques must be derived in order to properly deal with the singularity of the kernel term, which is related to the behavior of the elliptic integral functions. In previous works exact expressions are obtained for the integration of the kernel along wire cells, but as a major drawback they are expressed in terms of infinite summations, which are slowly convergent near the singular condition of the observation point. In this work, an alternative technique is proposed, using a decomposition of the singular elliptic function in terms of a polynomial expansion [4]. This method isolates the real singular term of the elliptic integral in a simple expression that can be performed analytically. The rest of the derived terms are regular, and numerical integration can be employed. Using this semianalytical approach, the different integrals involved in the evaluation of the electromagnetic fields can be evaluated with higher accuracy, as it will be shown in the communication.

Enhanced topology for the design of bandpass elliptic filters employing inductive windows and dielectric objects

This work presents a new topology for the design of bandpass elliptic filters employing inductive windows and dielectric objects. The proposed filtering structure combines, for the first time, the modified TE102 resonating mode with the modified TE201 mode. The TE201 mode is excited by placing a wide dielectric post inside a waveguide cavity. The main advantage of the new topology is that two transmission zeros can be synthesized in the insertion loss response of the filter, for a second order structure. Also there is a high flexibility on the location of the transmission zeros. They can be synthesized along the frequency axis for maximum selectivity, or as a pair of complex poles for phase equalization.

Compact implementation of transmission zeros using the zero shifting property

In this contribution we propose a structure for the implementation of transmission zeros using the zero shifting property. In previous implementations, two open loop resonators operating at different resonances were employed. In the configuration, one of the open loop resonators is substituted by a short-circuited transmission line, thus resulting into a more compact structure. Also, the new configuration is able to support larger bandwidth than traditional designs. This is due to an improved capability to increase the coupling between the input and output lines to the new short-circuited transmission line. For this purpose a new cross-shaped coupling structure is proposed. A manufactured prototype has been successfully tested. The results show the usefulness and validity of the new structure.

Novel Spatial Domain Integral Equation Formulation for the Analysis of Rectangular Waveguide Steps Close to Arbitrarily Shaped Dielectric and/or Conducting Posts

In this paper, a novel integral equation formulation expressed in the spatial domain is proposed for the analysis of rectangular waveguide step discontinuities. The important novelty of the proposed formulation is that allows to easily take into account the electrical influence of a given number of arbitrarily shaped conducting and dielectric posts placed close to the waveguide discontinuity. For the sake of simplicity, and without loss of generality, the presented integral equation has been particularized and solved for inductive rectangular waveguide geometry. In this case, the integral equation mixed-potentials kernel is written in terms of parallel plate Greens functions with an additional ground plane located on the waveguide step. Therefore, the unknowns of the problem are reduced to an equivalent magnetic surface current on the step aperture and equivalent magnetic and electric surface currents on the dielectric and conducting posts close to the discontinuity. The numerical solution of the final integral equation is efficiently computed after the application of acceleration techniques for the slowly convergent series representing the Greens functions of the problem. The numerical method has been validated through several simulation examples of practical microwave devices, including compact size bandpass cavity filters and coupled dielectric resonators filters. The results have been compared to those provided by commercial full-wave electromagnetic simulation software packages, showing in all cases a very good agreement, and with substantially enhaced numerical efficiencies.

Efficient novel IE analysis for inductive structures with obstacles attached to the waveguide walls

We present a novel efficient technique for the analysis of inductive structures containing metallic and dielectric obstacles, using a Surface Integral Equation (IE) formulation. Using the Surface Equivalence Principle, the main problem is divided into two subproblems. The first one is formulated with the parallel plate waveguide (PPW) Greens functions, and the second with the Greens functions of an unbounded homogeneous medium. The most important contribution of this paper is the consideration of obstacles attached to the waveguide walls. This situation requires a special treatment of the Greens functions of the second subproblem, by adding a spatial image with respect to the corresponding wall where the attachment is placed. This is essential in order to obtain adequate results, as it will be shown in further examples. Moreover, the presence of inductive dielectric posts connected to the walls inside cavity filters allows to obtain interesting elliptic responses, in addition to the possibility of reducing the multipactor risk for space applications.

Efficient Analysis of Inductive Multiport Waveguide Circuits using a Surface Integral Equation Formulation

This paper presents a simple and alternative approach for the analysis of inductive multiport waveguide microwave components. The technique uses a surface integral equation formulation to treat both metallic and dielectric objects inside the component structure. In order to avoid the relative convergence problem of other techniques based on mode matching, a novel port treatment is used. The technique is based on the application of the extinction theorem using the spatial representation of the Greens functions and image theory. Different complex H-plane structures are analyzed, including microwave bandpass filters with elliptic transfer functions and waveguide bends with dielectric posts. Results show the high accuracy and versatility of the new technique derived.