A Miniaturized Low-Profile Multilayer Frequency-Selective Surface Insensitive to Surrounding Dielectric Materials

In most applications, a frequency-selective surface (FSS) needs to be attached to a wide variety of dielectric materials. The performance of a traditional FSS is greatly influenced by the dielectric material to which it is attached. In this paper, a novel multilayer structure is proposed to construct an FSS. The performance of the proposed structure is shown to be very stable when it is attached directly to a wide variety of dielectric materials of arbitrary thickness. Both single- and dual-polarized structures are designed. The shape of the FSS element is designed by using stepped-impedance transmission lines. A new methodology is proposed to design the FSS by maximizing the value of the capacitance between adjacent layers. The proposed structure offers three distinctive advantages. First, the strong cross-layer capacitance makes the FSS element very compact. The dimensions of the miniaturized element are as small as $0.012 \lambda \times 0.012 \lambda $ . Second, for the proposed structure, the lower the profile, the stronger the cross-layer capacitance, and the lower the resonant frequency. This is unique to the proposed structure since the resonant frequency is usually higher for a lower profile for traditional structures. Third and most importantly, any external dielectric material attached to the FSS will not significantly affect the performance of the FSS due to this strong cross-layer capacitance. Through examples of a single-polarized bandpass FSS at 1 GHz and a dual-polarized bandpass FSS at 1.96 GHz, it is demonstrated that a stable resonant frequency under various incident angles up to 75° can be achieved.