Close coupled resonant aperture inserts for waveguide filtering applications

A two-layer frequency selective surface (FSS) is used as a very compact and lightweight transverse waveguide filter element. A narrow-band transmission response is produced from two layers, which, otherwise, in isolation would exhibit a broadband response. Measured results are compared with theoretical data obtained from a Transmission Line Matrix (TLM) based modeling method. Reduction in the passband bandwidth of a factor of four has been achieved using the proposed structure.