An array of square apertures in a conducting film behaves as a high-pass filter element. By contrast, an array of cross-shaped apertures exhibits bandpass behavior. We have investigated experimentally how variations in the pattern periodicity, the crossarm width, and the separation between the crosses alter the spectral behavior. We find that these bandpass filters can have excellent peak transmission and good shortwave rejection. The wavelength of peak transmission is determined by the length of the crossarm (and not by the array period itself), while the bandwidth is determined chiefly by coupling between the crosses. These results are qualitatively consistent with a coupled-dipole model. This model appears to have more utility for practical filter design than the commonly used transmission-line model.
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