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An accurate equivalent circuit model (ECM) for general multiwire multiorder printed circuit board (PCB) metagratings (MGs) is developed. The effective impedances of the grating wires are modeled as lumped loads in the ECM. The numerous propagating Floquet harmonics supported by the grating are modeled as circuit ports. Based on the desired field transformation for the MG, a set of required scattering parameters for its ECM is derived. The equivalent lumped loads are subsequently optimized to realize these parameters, which is analogous to shaping the diffraction pattern of the MG to match the desired functionality. Within this framework, it is possible to encode multiple functions into a single device by simultaneously optimizing all relevant entries of the ECM scattering matrix. Using the proposed technique, an angle-multiplexed multifunctional MG is designed and investigated. [ABSTRACT FROM AUTHOR]

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 $\lambda /75$ at the highest operating band (5.2 GHz), making the overall thickness extremely small. The unit cell size for the designs is about $\lambda /5$ at 5.2 GHz. The designs are fabricated and tested to validate the proposed methodology. [ABSTRACT FROM PUBLISHER]