Second-Order Terahertz Bandpass Frequency Selective Surface With Miniaturized Elements

In this paper, a second-order frequency selective surface (FSS) made of miniaturized elements is proposed and designed for terahertz applications. The FSS is composed of two layers of metallic arrays separated from each other by a polymer dielectric spacer. The unit cells on the front and back layers are smaller than <formula formulatype="inline"><tex Notation="TeX">$\lambda _{0}/5$</tex> </formula>, where <formula formulatype="inline"><tex Notation="TeX">$\lambda _{0}$</tex></formula> is the free space wavelength. The operation principle of the proposed FSS is described through a circuit model, and a synthesis procedure is presented for designing a desired filtering response. A prototype of the FSS is synthesized to operate at a center frequency of 0.42 THz with 45% fractional bandwidth. The designed FSS is fabricated by using microfabrication process. The performance is evaluated by using terahertz time-domain spectroscopy. Measurement results show a low sensitivity of the FSS response to oblique angles of incidence for both of the TE and TM polarizations.