Tri-band frequency selective surface with circular ring elements

A metallic ring has been proposed as the resonant element for a triband frequency selective surface (FSS). Dielectric substrate material with a high dielectric constant is employed to reduce the ring size and thus the element spacing for avoiding grating lobes at the highest frequency. A double-screen approach is used to yield better matching and therefore lower insertion loss for the transmission bands. Both a single-screen FSS design and a double-screen FSS design have been fabricated and tested for the triband system. Excellent agreement between calculation and measurement was achieved. The double-screen FSS provided better performance than the single-screen FSS at S- and Ku-band frequencies. By using the ring elements, the FSS's resonant frequency becomes very insensitive to a wide variation of incident angles.>