Antenna

A multi-frequency folded lens antenna structure comprising:

• a stack comprising,
• a polarization-dependent trans-reflector,
• a dielectric gap, and
• a multi-frequency twist-reflector;
• wherein the polarization-dependent trans-reflector is configured to transmit electromagnetic radiation of a first polarization incident from within the stack out of the stack and to reflect electromagnetic radiation of a second, different polarization incident within the stack towards the multi-frequency twist-reflector, and
• the multi-frequency twist-reflector is configured to selectively change a polarization of the reflected electromagnetic radiation from the second polarization to substantially the first polarization and to direct the electromagnetic radiation of substantially the first polarization, within the stack, towards the polarization-dependent trans-reflector for at least partial transmission out of the stack,
• wherein the multi-frequency twist-reflector is configured to selectively change the polarization for at least a first frequency band and for at least a second frequency band, non-contiguous to the first frequency band,
• wherein the multi-frequency twist-reflector comprises a periodic conductive surface that provides frequency selectivity, a dielectric layer, and a reflective surface,
• wherein the periodic conductive surface includes parallel, equally-spaced, discontinuous conductive strips defining conductive strip portions that are separated in a first direction, parallel to the conductive strips, by first gaps and are separated in a second direction, orthogonal to the first direction, by second gaps, wherein the first gaps have a constant first size, and the second gaps have a constant second size, the first size of the first gaps being smaller than the second size of the second gaps.