Showing papers by "Francisco Medina published in 2007"

Application of Total Least Squares to the Derivation of Closed-Form Green's Functions for Planar Layered Media

Abstract: A new technique is presented for the numerical derivation of closed-form expressions of spatial-domain Green's functions for multilayered media. In the new technique, the spectral-domain Green's functions are approximated by an asymptotic term plus a ratio of two polynomials, the coefficients of these two polynomials being determined via the method of total least squares. The approximation makes it possible to obtain closed-form expressions of the spatial-domain Green's functions consisting of a term containing the near-field singularities plus a finite sum of Hankel functions. A judicious choice of the coefficients of the spectral-domain polynomials prevents the Hankel functions from introducing nonphysical singularities as the horizontal separation between source and field points goes to zero. The new numerical technique requires very few computational resources, and it has the merit of providing single closed-form approximations for the Green's functions that are accurate both in the near and far fields. A very good agreement has been found when comparing the results obtained with the new technique with those obtained via a numerically intensive computation of Sommerfeld integrals

Design of Wide-Band Semi-Lumped Bandpass Filters Using Open Split Ring Resonators

Abstract: Open split ring resonators (OSRRs) are used in this letter to design wide-band semi-lumped bandpass filters. OSRRs work as lumped LC series elements due to their small electrical size and can be then used as building blocks of reduced size band pass filters. The values of the capacitance, C, and inductance, L, of the OSRR are controlled by adjusting the geometrical parameters of the coupled open rings. In our design, the OSRRs are connected through quarter-wave lines which act as inverters. The impedance of these inverters have been conveniently calculated to achieve the filter specifications. Finally bending and/or meandering techniques have been applied so as to obtain highly compact designs. Experimental verification is provided and good agreement has been found between electromagnetic simulations and measurements

Design of Compact Low-Pass Elliptic Filters Using Double-Sided MIC Technology

Abstract: A novel implementation of stepped-impedance low-pass elliptic filters is presented in this paper The filters are based on the well-known technique of cascading high- and low-impedance sections to simulate the ladder LC lumped-circuit prototype We propose in this study a new approach to build up the constitutive circuit elements by taking advantage of the use of both sides of the substrate The use of double-sided technology yields both design flexibility and good circuit performance High-impedance sections are achieved by using slots in the backside of the substrate, whereas low-impedance sections are obtained with parallel-plate capacitors In order to achieve the transmission poles corresponding to the elliptic design, these capacitors are series connected to the ground plane by means of high-impedance coplanar-waveguide lines, which mainly act as inductors As a final step, meandering techniques have been applied to the high-impedance sections of the filter to reduce the overall circuit size The measurement of several fabricated filters shows fairly good agreement between theory and experiment

Low-pass Elliptic Filters Using Mixed Microstrip-CPW Technologies

Abstract: Stepped-impedance low-pass elliptic fllters are presented in this paper which make use of patterning of both sides of the microstrip substrate. Microstrip and coplanar waveguide components as well as their interactions are used jointly to synthesize the required fllter elements. Relatively compact implementations with good electrical performance are obtained in this way. Conventional stepped-impedance low pass fllters (SI-LPF) consist of a cascading of electrically short high and low impedance sections to approximate the corresponding ladder LC lumped circuit prototype (1). However, this kind of fllter inherently presents two problems. One of them is the degradation of the stop band rejection level because of the frequency-distributed behavior of the flnite section lines. The second problem comes from the limits imposed by the microstrip technology to achieve very narrow strip widths and, consequently, high impedance section lines.

Microstrip Coupled Line Filters with Spurious Band Suppression

Abstract: Passband microstrip coupled line fllters are widely used in daily microwave en- gineering practice. These fllters present an undesired pass band at twice the design central frequency of the fllter. Two simple methods to suppress this drawback are reported in this com- munication. The proposed methods, apart from removing the spurious band, provide an extra coupling mechanism that relaxes tolerances of strip width and spacing in those cases where tightly coupled sections are required. DOI: 10.2529/PIERS060822161838 Parallel coupled lines microstrip fllters (PCMF) are well known devices in microwave practice. When implemented in their traditional form, i.e.,using a single layer substrate in microstrip tech- nology, these fllters present two relatively serious drawbacks. First, a spurious pass band appears at 2f0 (f0 is the central frequency of the fllter). The second problem comes from the di-culty of fabricating wide band fllters because of the weak coupling between the lines in the conventional structure. Strong coupling required by some fllter speciflcations leads to very small values of strip width, w, and strips spacing, s, which can not be sometimes accurately achieved in practice.

Mediation strategies in collective bargaining: self-reported and observational approach

Abstract: In this paper the effectiveness of mediation strategies is analyzed in two different types of collective labour conflicts: rights conflicts and conflicts of interests. Considering the relevance of triangulation and convergence of evidence (Carnevale & De Dreu, 2005; Carnevale & De Dreu, 2004) two complementary studies were conducted with different methodologies: self-reported measures and observation of mediation cases. In the study with self-reported measures the participants were professional labour mediators of the Extrajudicial System for Labour Conflict Resolution in Andalusia who completed a survey about the strategies they used and the outcomes they achieved in their most recent mediation intervention. In the observational study 26 mediation cases of this system were observed, randomly selected during the period when observations were carried out. 42,31% were conflicts of interests and 57,69% rights conflicts. Results suggest that contextual strategies oriented to manage the mediation process are effective in both types of conflicts. In the same way, substantive strategies oriented to deal directly with the issues in dispute are effective in both types of conflict. Reflexive strategies oriented to gain disputants trust and acceptance of the mediator and the mediation process were dysfunctional for effectiveness particularly in rights conflicts.

Solving the EFIE for printed layered structures with ferrite layers

Abstract: This work presents a mixed-potential integral equation (MPIE) posed in the space domain to deal with printed structures whose layered substrate includes arbitrarily magnetized ferrite materials. Previous to solving the MPIE it is presented a method to numerically generate the appropriate Green's functions starting from their spectral-domain counterparts. The corresponding reaction integrals of the method-of-moments matrix are accurately computed by means of appropriate techniques that deal efficiently with the singular and quasi-singular integrals. The proposed approach gives rises to a method that, although very demanding from a numerical point of view, is able to analyze planar structures with ferrite layers and non-rectangular shape conductors.