Automated design of frequency selective surfaces with the application to Wi-Fi band-stop filter

Abstract

This article presents a technique for analysis and automated design of frequency selective surfaces. In this work the method of moments is used to analyse a planar periodic structure. The approach allows to automate the whole process of the filter design and frees the users from the detailed knowledge of the filter design theory. For the practical part of the paper, the algorithm of Levenberg-Marquardt is chosen as a local optimisation method. Whole process of automation is implemented in Matlab. An optimisation of a band-stop filter for Wi-Fi signals serves as a practical example. A Wi-Fi device communicating under standard 802.11b or 802.11g uses a specific channel which has frequency between 2.412 and 2.484 GHz. Therefore the goal is to design a band-stop filter which ideally does not transmit mentioned band of frequencies. The geometry of Jerusalem-cross serves as a structure to be optimized. Four design variables are defined for optimisation: the width and the height of a periodic cell (a square), the width of an arm and two other variables which influence the length of an outer arm and the length of the whole structure of the Jerusalem-cross. This filter consists of two dielectrically separated conductive layers which make the filter more narrow-band. S-parameters of the final optimized geometry of the Wi-Fi filter are presented in the paper.