A novel active frequency selective surface (FSS) is presented for 2.45 GHz applications. It consists of circular aperture elements with four PIN diodes placed orthogonal to each other on FR4 substrate. The negative dc biasing is provided with cross shaped supply lines from the reverse side of the substrate, while positive biasing is provided from the front side of printed circular structure. This active FSS design enables transmission to be switched on or off at 2.45 GHz, providing high transmission when the diodes are in OFF state, and high isolation when the diodes are ON. The design also provides very good stability to oblique TE incidence, i.e perpendicular polarisation.