A new neural network technique for the design of multilayered microwave shielded bandpass filters

In this work, we propose a novel technique based on neural networks, for the design of microwave filters in shielded printed technology. The technique uses radial basis function neural networks to represent the non linear relations between the quality factors and coupling coefficients, with the geometrical dimensions of the resonators. The radial basis function neural networks are employed for the first time in the design task of shielded printed filters, and permit a fast and precise operation with only a limited set of training data. Thanks to a new cascade configuration, a set of two neural networks provide the dimensions of the complete filter in a fast and accurate way. To improve the calculation of the geometrical dimensions, the neural networks can take as inputs both electrical parameters and physical dimensions computed by other neural networks. The neural network technique is combined with gradient based optimization methods to further improve the response of the filters. Results are presented to demonstrate the usefulness of the proposed technique for the design of practical microwave printed coupled line and hairpin filters

Numerical evaluation of the Green's functions for arbitrarily shaped cylindrical enclosures and their optimization by a new spatial images method

IIn this paper, a spatial image technique is used to efficiently calculate the mixed potential Green’s functions associated with electric sources, when they are placed inside arbitrarily shaped cylindrical cavities. The technique is based on placing electric dipole images and charges outside the cavity region. Their strength and orientation are thencalculated by imposing the appropriate boundary conditions for the fields at discrete points on the metallic wall. A method for the assessment of the potentials accuracy is proposed, and several optimization techniques are presented. Three cavities are analyzed to demonstrate the usefulness of the techniques. The cutoff frequencies and potentials patterns are compared to those obtained by a standard finite elements technique, showing excellent agreement. Finally, a band-pass filter based on coupled lines is analyzed, demonstrating the practical value of the technique.This work has been developed with support from the Spanish National Project (CICYT) with reference TEC2004-04313-C02-02/TCM, and the Regional Seneca Project with reference 02972/PI/0

Efficient Calculation of the Green's Functions for Multilayered Shielded Cavities with Right Isosceles-Triangular Cross-Section

An efficient calculation of the Green’s functions inside multilayered shielded cavities with right isosceles-triangular cross-section is presented. The method is entirely developed in the spatial domain, and it is based on image theory. The idea is to use the spatial-domain Green’s functions inside a multilayered shielded square box, in order to accurately obtain the Green’s functions for the right isosceles-triangular cavity. Image theory is then used to enforce the boundary conditions along the non-equal side of the triangle. It is shown that the new algorithm is very robust, with limited computational effort. Resonance frequencies and potential patterns of a triangular cavity have been calculated and compared with those obtained by other techniques, showing very good agreement. Finally, a transversal filter inside a multilayered triangular-shaped cavity is designed, manufactured and tested using the developed technique.This work was partially supported by the Spanish Ministry of Education and Science under Grant FPU-AP2006-015 and with the Project TEC2007-67630-C03-02

Repeat tourism in Uruguay: modelling truncated distributions of count data

This paper studies the determinants of repeat visiting in Uruguay, where loyal visitors are a relevant part of the total. From a statistical point of view the number of times a visitor has been to a place constitutes count data. In this regard available information on Uruguay present relevant limitations. Count data is in fact reported only for those who visited the country up to five times, whereas records about the most frequent visitors are collapsed into one residual category. This implies that the classic models for count data such as Poisson or negative binomial cannot be put into consideration. The paper suggest instead the use of a quantile count data regression, that is a model based on measures of location rather than mean values. A set of explanatory variables related to socioeconomic characteristics, features of the journey and composition of the travel party are considered

Repeat tourism in Uruguay: modelling truncated distributions of count data

This paper studies the determinants of repeat visiting in Uruguay, where loyal visitors are a relevant part of the total. From a statistical point of view the number of times a visitor has been to a place constitutes count data. In this regard available information on Uruguay present relevant limitations. Count data is in fact reported only for those who visited the country up to five times, whereas records about the most frequent visitors are collapsed into one residual category. This implies that the classic models for count data such as Poisson or negative binomial cannot be put into consideration. The paper suggest instead the use of a quantile count data regression, that is a model based on measures of location rather than mean values. A set of explanatory variables related to socioeconomic characteristics, features of the journey and composition of the travel party are considered

Analysis of inductive multiport microwave devices employing a novel double parallel plate approach

The authors present a novel surface integral equation approach to analyse inductive microwave devices with several parallel input­ output ports containing inductive metallic and dielectric obstacles. The technique decomposes the main problem into three subproblems, employ- ing different kinds of Green's functions. One of the subproblems uses the classical Green's func- tions of an infinite unbounded medium with the constitutive parameters of the dielectric obstacles. A novel point of the technique is the formulation of the two other subproblems with two different, 908 rotated parallel plate regions. In these regions the parallel plate waveguide Green's functions are used to simplify the modelling of the excitation problem. The second novel aspect of the work is in the treatment of these Green's functions, to smooth their behaviour, and to improve their con- vergence. Several numerical results are presented to demonstrate the usefulness of the algorithms proposed. Also, several results for inductive microwave devices are presented to show the practical value of the approach.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02. Fundación Séneca, Ref. 08833/PI/0

A novel low-pass filter based on dielectric impedance inverters to enhance the multipactor breakdown threshold

This work presents a novel low-pass filter based on using dielectric materials, in the critical areas of the structure, to prevent high-power space condition adverse effects, like multipactor breakdown. It is shown that the use of dielectric pieces in the inverters of the filter leads to increased gaps between metallic parts in the irises. In addition, by completely filling up the air space in critical gaps, the multipactor breakdown thresholds can be increased. Moreover, they also lead to a volume reduction, increasing compactness of the structure. To demonstrate the proposed concept, a prototype has been manufactured with an aluminum housing and a Teflon dielectric material, and tested for multipactor effect at ESA-VSC Laboratory. Tests confirmed that the manufactured filter has good electrical performance with cut-off frequency 13.6 GHz, insertion losses 0.32 dB, return losses better than 15 dB, and additionally does not show multipactor breakdown up to the maximum power tested in the experimental facility (5.5 kW).This research work has been financially supported by the Spanish Ministerio de Ciencia e Innovación in the frame of the project “Green an Efficient Technologies for Advanced Telecommunication Systems (GRETAS)” with Ref. TPID2019-103982RB-C42

Numerical evaluation of the Green's functions for arbitrarily shaped enclosures

In this paper, a new spatial method has been implemented for the efficient calculation of the mixed potential Green's functions associated to electrical sources, when they are placed inside arbitrarily-shaped cylindrical cavities. The technique consists of placing electric dipole images and charges outside the cavity, imposing, at discrete points of the metallic wall, the appropriate boundary conditions for the potentials. Results show that the numerical convergence is attained fast. The cut-off frequencies and potential patterns for a trapezium-shaped waveguide are compared to those obtained by a standard finite elements technique, showing excellent agreement. Furthermore, a printed planar filter shielded in a square cavity has been analyzed with the new Green's functions, showing the practical value of the new theory.This work has been supported by Spanish National project CICYT-TEC2004-043 13-C02-02/TCM, and by Fundacion Séneca project, Ref. 02972/PI/0

Use of ground planes within the spatial images technique: Application to the analysis of rectangular multilayered shielded enclosures

The use of ground planes is proposed inside the spatial images technique in order to calculate the multilayered shielded Green's functions for rectangular enclosures. The positions of the ground planes are dynamically located, covering two walls of the cavity, as a function of the source position. Spatial mirror images, related to the ground planes, are used to perfectly impose the boundary conditions along these cavity walls. This completely removes the problems associated to the singular behavior of the source when it is placed close to a wall or a corner, improving numerical stability. In addition, the method leads to a very efficient computation (about 15 times faster than the original approach), due to the reduced number of non-mirror images that must be effectively computed. A multi-band filter in hybrid waveguide-microstrip technology is analyzed with the new method, showing excellent agreement with measured data.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02. Fundación Séneca, Ref. 08833/PI/08