A. L. Gutiérrez

Multilayer FSS Optimizer based on PSO and CG-FFT

Traditionally, Frequency Selective Surfaces (FSS) are designed to produce a certain spectral response, in one or more frequency bands, using a methodology that manually tunes and simulates the behavior of the structure. In some cases, due to the high filtering requirements of an application, it could be necessary make FSS with several periodic surfaces, in order to improve the frequency response of the final prototype. This process is difficult to be carried out if the filtering response to synthesize cannot be directly obtained with a combination of classical FSS unit cell geometries. To overcome this problem, in this paper a methodology of optimization that automates the hard and costly search is introduced, combining the PSO and an analysis methodology of structures with several periodic surfaces that act as the cost function: the Conjugate Gradient Fast Fourier Transform (CG-FFT). This approximation uses a multilayer Green function calculated applying the transmission line model that considers the mutual coupling effects by translating the field from the source FSS to the other periodic surfaces. Representative results including the optimization of a three layer FSS with two planar periodic surfaces are reported and discussed in order to show the usefulness of the approach proposed.

Coverage optimization in single frequency Networks using simulated annealing

In the last years, the migration from analog to digital terrestrial television systems has favored the deployment of Single Frequency Networks (SFN), more efficient from a spectrum point of view, to provide DVB-T services in larger geographical areas through the reuse of frequencies. However, the planning of a SFN is not a trivial task, since the designer must find a trade-off between the quality of service (QoS) required in a geographical area and the overall cost involving the deployment and maintenance of such a network, which depends primarily on the number of transmitters needed and their power. In this work, a simulated annealing (SA) based approach applied to improve the overall coverage in a SFN by optimizing transmitters parameters such as the static delay or the gain and orientation to be applied to the sector antennas, is presented. For this purpose, the approach is divided into three blocks that work as a whole: A) A propagation prediction tool, B) A receiver behavior modeling, including different methods for the FFT window positioning and echoes combination, and C) SA, used to improve the coverage over the desired area according to certain QoS requirements. Results for two SFN are included in order to demonstrate the usefulness of the method.

Analysis of single layer multiple concentric ring elements in reflectarray antennas

In this paper, multiple concentric rings are considered as phase elements in reflectarrays and the benefits of these single layer rings are compared to conventional reflective structures (multi and single layer, rectangular or elliptical printed patches) when applied to the design of reflectarrays. These ring-shaped structures have got, as the main advantages, the ease of manufacture and the wide range of phase obtained, exceeding easily 1000 degrees. The analysis of the structures is made by means of the CG-FFT method. The simulations are carried out in the Ku band, the one commonly used in Direct Broadcast Satellite applications (DBS). In order to determine the effect of the manufacturing tolerances, results of a test carried out with a simulated reflectarray are included, using a PSO based algorithm to perform the phase synthesis.