Frequency selective surface with repeating pattern of concentric closed conductor paths, and antenna having the surface

An antenna comprising a reflector, a frequency selective element, and a plurality of microwave feeds positioned for illuminating said reflector wherein a first of said feeds operative at a higher frequency of radiation is located on a side of said frequency selective element opposite said reflector to permit illumination of said reflector by transmittal of radiation through said frequency selective element, and wherein a second of said feeds operative at a lower frequency of radiation and said reflector are positioned on a common side of said frequency selective element opposite said first feed for permitting illumination of said reflector by reflection of radiation at said lower frequency by said frequency selective element, and

• wherein said frequency selective element comprises:
• a substantially periodic array of sets of radiators disposed along a surface of said element, wherein each of the sets of the radiators comprises at least two radiators of which one radiator is an innermost radiator and a second radiator is an outermost radiator which encircles the innermost radiator, each of said radiators having a configuration which encircles a point on the surface of said element;
• and
• wherein the outermost one of said radiators has a circumference approximately equal to a wavelength of the radiation at said lower frequency, said sets of radiators being spaced apart by a spacing equal approximately to one-half wavelength of the radiation at said lower frequency.