Abstract: A structure for selectively transmitting electromagnetic energy therethrough which comprises a relatively thin insulative substrate having front and rear surfaces. The surfaces each have a pattern of regions thereon in each of which a first metallized Jerusalem cross is formed. In each region additional metallized Jerusalem crosses are formed in each of the quadrants of the first Jerusalem cross. The dimensions of the Jerusalem crosses on each surface are selected to provide suitable transmission resonances so as to permit transmission of electromagnetic energy through the surface over a selected portion of the frequency spectrum and to prevent transmission outside said portion of the spectrum.