Wireless Communication Desense Due to Electromagnetic Shields

Abstract

EM shields are commonly used to prevent unwanted radiations and isolate the electronic devices from outside environment. In this paper, we show EM shields may cause the degradation of wireless communication performance if not carefully deigned. In the presented wireless system, the resonance frequency of EM shield is within the range of Wi-Fi communication band. The thermal pad inside the EM shield has high dielectric constant that reduces the resonance frequency from above the operating frequency band to inside the band. Also, the certain harmonic of digital clock happens to be at the resonance frequency of the EM shield. Therefore, the harmonic spur couples to Wi-Fi chains of communications through resonance of EM shield and degrades the sensitivity of Wi-Fi receivers. We will discuss the mechanism of EM coupling and how to alleviate the system performance degradation through a few mitigation techniques. The dielectric constant of the thermal pads inside the EM shield should be chosen carefully to prevent the coupling through EM shield or external radiation.