The active frequency selective surface can be applied as precision instrument housing. It will adapt to the environmental changes and self adjust the frequency of the passband, thus achieving the filtering purpose, which lowered the interfaces coming from the environment without causing any disruption to the device. This article applies the technology of using four sides slit loaded PIN diode, designed a new active frequency selective surface, the passband is between 0.6 GHz to 3.2 GHz, and ensured the tran...