Frequency-selective surfaces with multiple apertures within a periodic cell

We discuss a method for analyzing frequency-selective surfaces (FSS’s) consisting of an array of multiple apertures or patches per unit periodic cell. Based on the modal method, our method is unique in that the multiple apertures or patches within a unit cell need not be identical in size or shape. Applying our technique to thin perfectly conducting sheets perforated with patterns of varying-length narrow rectangular apertures, we demonstrate a pattern of slot apertures that produces a double-resonance spectral transmission profile.