Abstract: A planar antenna for circular polarized microwaves incorporates a substrate sandwiched between conductive layers having a plurality of openings arranged in a rectangular array, with a pair of perpendicular excitation probes supported on the substrate in alignment with each opening, and a feed circuit for interconnecting the excitation probes in a predetermined phase relationship. Two additional conductive elements may be supported on the substrate in alignment with the excitation probes to provide improved impedance matching. The feed circuit may incorporate a pair of quarter wavelength feed lines connected to the excitation probes, with a resistance element interconnected between the feed lines. The feed point of the antenna may be located near the center of the array, occupying a position normally occupied by one of the pairs of excitation probes.

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.