A Technique for Designing Multilayer Multistopband Frequency Selective Surfaces

A systematic technique for designing and optimizing multilayer frequency selective surfaces (FSSs) with low overall profile is presented. Periodic scatterers in the shape of loaded dipoles (dogbones) are used on each layer to create a single-stopband response. Multiple such layers are cascaded together to create the desired multistopband response. An equivalent circuit model for a multilayer FSS that explicitly and intuitively accounts for electromagnetic coupling interactions between the layers is proposed and investigated. This model is used in a novel design method, which precompensates for the effect of coupling during circuit-based design stage rather than postcompensating through iterative full-wave (FW) optimization after the design stage, as in most traditional approaches. As a consequence, this approach has the potential to greatly speed up the design process by enabling considerable simplifications during FW simulations. The proposed method is used to design several ultralow-profile triple-layer, triple-stopband surfaces intended for Wi-Fi applications. The interlayer spacing is as low as λ/75 at the highest operating band (5.2 GHz), making the overall thickness extremely small. The unit cell size for the designs is about λ/5 at 5.2 GHz. The designs are fabricated and tested to validate the proposed methodology.