We propose a novel design of a true 3D chiral metasurface behaving as a spatial polarization converter with asymmetric transmission. The metasurface is made of a lattice of metallic sesquialteral (one and a half pitch) helical particles. Each particle contains six rectangular bars arranged in a series one above the another creating a spiral. The proposed metasurface exhibits a dual-band asymmetric transmission accompanied by the effect of a complete polarization conversion in the response on the particular distributions of currents induced in the particle's bars by an incident wave. Regarding circularly polarized waves the metasurface demonstrates a strong circular dichroism. A prototype of the metasurface is manufactured for the microwave experiment by using 3D-printing technique utilizing Cobalt-Chromium alloy, which exhibits good performances against thermal fatigue and corrosion at high temperatures. Our work paves the way to find an industrial solution on fabricating communication components with efficient polarization conversion for extreme environments.

Transmission of linearly and circularly polarized waves is studied both theoretically and experimentally for chiral metasurface formed by an array of metallic square helices. The helical particles of the metasurface are constructed of rectangular bars manufactured with the use of direct 3D printing in solid metal. It is found that transmittance of the metasurface depends critically on number of bars forming the square helical particles. In the case of even number of bars, chiral metasurface exhibits the identical co-polarized transmittance of orthogonal linearly polarized waves, which are characterized by a dual-band asymmetric transmission. In the case of odd number of bars, the metasurface provides the same crosspolarization conversion for any polarization orientation of the incident field and thus serves as a polarization-independent twist polarizer. Transmittance of this polarizer is investigated with respect to the dimensions of square helices. It is shown that chiral metasurface under investigation is characterized by strong broadband circular dichroism without regard to the number of bars used in the helical particles. A wide variety of transmission properties of such a metasurface makes it particularly attractive for use in polarization conversion and separation devices.