Secure Electromagnetic Buildings Using Slow Phase Switching Frequency Selective Surfaces

The concept of a secure electromagnetic building which can successfully prohibit wireless communications is presented. Wireless security is achieved using a slow phase switching technique and can be realized by time varying the transmission properties of a frequency selective surface to increase the bit error rate of the unwanted signal. Results are presented which demonstrate that a technique of phase switching at rates much lower than the baseband data rate can be used successfully. The system has been implemented using a reconfigurable dual polarized dual layer frequency selective surface incorporating varactor diodes where over 100° of phase change can be achieved for voltage changes of ±0–3V. A vector signal analyzer was used to evaluate the bit error rate performance of the system for a GSM signal operating at 2GHz. Bit error rates are shown to be as high as 36% which are sufficient to successfully prohibit wireless communication. The solution is also shown to be robust over a wide range of incidence angles which is important for real world applications where the location of the prohibited wireless source may be unknown or mobile. Furthermore, as the system is reconfigurable the building can be switched between a secure and non-secure mode.