Frequency Selective Surface Based Reflecting Screens for Improving Indoor Wireless Communication.

A dual band stop resistive type frequency selective surface (FSS) is presented in this paper for enhancing wireless signal coverage in indoor environments. The main problem of the passive FSS is when once it has been designed practically, it does not allow the duplicate or other different frequency behavior from it. To get rid of this important problem, the use of active elements (like PIN diode, Varactor diode, LDR) in the FSS is a very useful solution. FSS loaded by LDR is considered as reconfigurable surface to the EM wave dependent on intensity of light incident on it. The intensity of the light changes the resistance value of the LDR and thus the induced current path resistance varies. Here the effect of the resistance value in the induced current path of the FSS is being discussed in the article. The unit cell of the proposed FSS consists of two concentric square ring-shaped patches. Four resistive elements are loaded on each square ring. The effect of the variation in the resistance values of these elements on the transmission characteristics of the FSS is studied in detail. The proposed FSS shows dual band stop characteristics at 2.4 GHz and 4.95 GHz. By changing the resistance values $(0.1 \Omega, 10 \Omega, 50 \Omega$ and $100 \Omega)$ of the resistive elements in the inner and outer loop of the proposed design a tunable behavior of the frequency characteristics of the proposed design has been achieved. Reflective screens based on the proposed design can be used on building walls for improving wireless communication in complex indoor environments.