Fernando Daniel Quesada Pereira

Two compact configurations for implementing transmission zeros in microstrip filters

This contribution presents compact structures for the implementation of transmission zeros using the zero shifting property. First, two open-loop resonators operating at different resonances are employed. Then, one of the open-loop resonators is substituted by a (/spl lambda//4) short-circuited transmission line, thus resulting into a more compact structure. Properties of these configurations are discussed, and two manufactured prototypes have been successfully tested. The results show the usefulness and validity of the new structures with high rejection capabilities.

A neural network method for the analysis of multilayered shielded microwave circuits

In this paper, a neural-network-based method for the analysis of practical multilayered shielded microwave circuits is presented. Using this idea, a radial basis function neural network (RBFNN) is trained to approximate the space-domain multilayered media boxed Greens functions used in the integral-equation (IE) method. Once the RBFNN has been trained, the outputs of the neural network (NN) replace the exact Greens functions, during the numerical solution of the IE. The computation of the RBFNN output values is very fast in comparison with the numerical methods used to calculate the exact Greens functions. This paper describes two novel strategies for efficiently training the RBFNN. In the first strategy, the input space of the RBFNN is divided into several spatial and frequency regions. The spatial subdivision is extended for the first time to both observation and source regions. In addition, the subdivision of the observation points regions is applied in a novel manner to the whole cross section of the metallic box. The second strategy combines the above region subdivision with an adaptive selection of the neurons variances in each region. The accuracy and the computational gain achieved with the NN method proposed makes possible the implementation of computer-aided-design tools that can be used for the analysis and design of integrated shielded microwave circuits (e.g., monolithic microwave integrated circuit devices) on a real-time basis

Efficient Analysis of Arbitrarily Shaped Inductive Obstacles in Rectangular Waveguides Using a Surface Integral-Equation Formulation

In this paper, we propose to use the surface integral-equation technique for the analysis of arbitrarily shaped H-plane obstacles in rectangular waveguides, which can contain both metallic and/or dielectric objects. The Greens functions are formulated using both spectral and spatial images series, whose convergence behavior has been improved through several acceleration techniques. Proceeding in this way, the convergence of the series is not attached to the employment of any particular basis or test function, thus consequently increasing the flexibility of the implemented technique. In order to test the accuracy and numerical efficiency of the proposed method, results for practical microwave circuits have been successfully compared with other numerical approaches

Numerical evaluation of the Green's functions for cylindrical enclosures by a new spatial images method

A spatial images technique is used to efficiently calculate the mixed potential Greens functions associated to magnetic sources when they are placed inside a circular cylindrical cavity. The technique places magnetic dipole images and charges outside the cylindrical region. Their strength and orientation are then calculated by imposing the appropriate boundary conditions for the fields at discrete points of the metallic wall. In this paper, the basic technique is combined with spatial domain multilayered Greens functions formulated with Sommerfeld integrals. This allows the analysis of practical multilayered circuits shielded in circular cavities. Convergence results are shown to demonstrate the usefulness of the technique. Two practical microwave circuits are also analyzed to show the validity of the formulation.

A Novel Efficient Technique for the Calculation of the Green's Functions in Rectangular Waveguides Based on Accelerated Series Decomposition

A new efficient technique for computing the Greens functions inside rectangular waveguides is presented. After a summary of the classical approaches and their difficulties, a new strategy is proposed, based on the decomposition of the main spectral series into simpler terms. Although the resulting series present better convergence rate, several acceleration techniques are combined to further improve the efficiency. Several results are presented to demonstrate the improvements in convergence rates obtained using the new decomposition.

A Novel Low-Pass Filter Based on Rounded Posts Designed by an Alternative Full-Wave Analysis Technique

A new low-pass waveguide filter topology is proposed based on capacitive posts using rounded shapes. The new structure is designed using a technique that benefits from a full-wave integral equation simulation tool for arbitrarily shaped capacitive microwave circuits. This integral equation method enables one to apply an efficient filter design technique employing iris geometries other than rectangular discontinuities, such as the one based on rounded posts proposed in this work. A prototype using circular posts has been manufactured and measured obtaining excellent results as compared with predictions, thus demonstrating the practical feasibility of the new proposed filtering structure. A new filter using elliptic capacitive posts was compared in terms of multipactor risk against similar filters based on traditional rectangular windows and on rectangular posts. Simulation results indicate that the new proposed concept using rounded shapes leads to geometries that can double multipactor thresholds as compared with traditional filters.

Design of Bandpass Elliptic Filters Employing Inductive Windows and Dielectric Objects

In this paper, we propose an alternative configuration for the design of bandpass inductive filters using transversal topologies. The structure is based on the use of a dielectric post asymmetrically placed on a cavity resonator. The input and output windows will couple energy to the TE102-and TE103 -mode resonators at the same time, therefore obtaining the transversal topology. The proposed configuration is very compact, and allows to implement transmission zeros for maximum selectivity in an easy way. Results are validated with Ansofts finite-element High Frequency Structure Simulator tool, and with an integral-equation technique to demonstrate the validity of the proposed structure.

Investigation of Multipaction Phenomena in Passive Waveguide Filters for Space Applications

This paper presents an investigation on multipaction risk in microwave bandpass filters. The study reveals higher multipaction risk for narrower bandpass filters. To alleviate the problem with multipaction generation, different filtering structures are proposed. Results demonstrate that using the new structures multipaction risk can be reduced as much as 30% with regard to the initial design

Optimization-Oriented Design of RF/Microwave Circuits Using Inverse-Linear-Input Neuro-Fuzzy-Output Space Mapping With Two Different Dimensionality Simulators

In this paper, an efficient optimization technique aligning three-dimensional (3-D) electromagnetic simulator responses with two-dimensional (2-D) electromagnetic simulator responses around space mapped solution, for the electromagnetic design of radiofrequency and microwave 3-D circuits is presented. The interface between 2-D and 3-D electromagnetic simulators is obtained from an inverse linear input space-mapping approach and an output modeling process based on a fuzzy logic technique. It is shown that the technique provides a highly accurate estimation of the 3-D design parameter space of the 3-D radiofrequency and microwave circuits to be designed, for initially fixed design specifications. Designs of first-order, second-order and sixth-order C-band 3-D evanescent rectangular waveguide bandpass filters with dielectric posts show the performance of our approach.

ANALYSIS OF INDUCTIVE WAVEGUIDE MICROWAVE COMPONENTS USING AN ALTERNATIVE PORT TREATMENT AND EFFICIENT FAST MULTIPOLE

This paper presents a simple and alternative approach for the analysis of inductive waveguide microwave components. The technique uses a surface integral equation formulation, in which the contours of the waveguide walls and of the inner obstacles are all discretized using triangular basis functions. In order to avoid the relative convergence problem of other techniques based on mode matching, an alternative port treatment is used. The technique is based on the application of the extinction theorem using the spatial representation of the Greens functions in the terminal waveguides. In addition, the Fast Multipole Method is proposed in order to reduce the computational cost for large problems. Different complex structures are analyzed, including microwave bandpass filters with elliptic transfer functions, waveguide bends and T-junctions. Results show the high accuracy and versatility of the technique derived.