A new narrow band frequency selective surface geometry design at the unlicensed 2.4-GHz ISM band

Wireless devices in the unlicensed instruments, scientific, and measurements (ISM) bands cause mutual interference in indoor environments. This interference degrades the system performance and compromises security. Transforming existing building walls to a band stop frequency selective surface (FSS) can be an efficient solution for such problems. This work is proposed to design FSS for interference mitigation and network security within the buildings in the unlicensed 2.4-GHz ISM band and to provide maximum transparency at broadcast frequencies. A 2.4-GHz ISM band is a relatively narrow band which cannot be met by a conventional FSS for a wide range of incidence angle. Whereas wireless signals in indoor environment have a wide range of incidence angle. To obtain the desired narrow band response, a new FSSs element geometry is introduced which has a stable frequency response for TE polarization when the angle of incident wave is varied from 0° to 70°. HFSS software is used for simulation and design purposes. The obtained simulation and measurement results show that desired frequency response is achieved for TE polarization successfully.