Oblique Incidence Performance of an Active Square Loop Frequency Selective Surface

Oblique incidence performance of an active square loop frequency selective surface (FSS) is investigated. The design shows a stable frequency response for both parallel (TM) and perpendicular (TE) polarizations for incidence angles up to 60deg. Four PIN diodes have been placed orthogonal to each other in the FSS unit cell to provide a stable frequency response for both TE and TM. To minimise the effect of bias lines on the overall frequency response, a diagonal DC bias line, which is connected to the centre of the FSS unit cell, has been placed on the rear surface of the dielectric substrate. The design has good isolation between transmission and reflection states, which are controlled electronically by switching PIN diodes between ON and OFF states. Preliminary theoretical results are described.