Abstract:
Conventional techniques are used for polarization conversion including the use of natural materials and later artificial materials like metamaterials and multi-layered metasurfaces which cause issues like bulky size, narrow bandwidth and fabrication losses which make them incompatible for practical use. As a result, scientists have considered using ultra-thin metasurfaces to create miniaturized polarization manipulating devices that can operate across a wide range of frequencies with less volume and low losses. Chiral metasurface, which is subclass of metasurface, having chirality in its design leads to outstanding EM properties like asymmetric transmission and linear to circular polarization conversion with wide-band functionality which are highly desirable and can be utilized in the different satellite communication applications as polarization controlling device.
The aspect of asymmetric transmission (AT) that allows a medium to pass the EM waves in one direction while having restriction in the opposite direction, adds an additional degree of freedom in order to facilitate one way communication functionality. The proposed metasurface achieves linear to circular (LTC) polarization conversion with wideband AT functionality. This is accomplished for frequencies below 18 GHz using a bi-layered metasurface structure consisting of mutually twisted split ring resonators (SRRs). Towards chirality realization, the proposed metasurface top and bottom layers have a 90˚ rotation angle. For the frequency band of 13.31-13.81 GHz, the transmission goes up to – 4.3 dB. The maximum polarization extinction ratio (PER) of -51 dB has been achieved for the 492 MHz bandwidth at 13.55 GHz. The relatively simple structure, and the wide bandwidth enabled by using a bilayer metasurface, makes the proposed structure a prominent design as a polarization conversion device that can be used in satellite communications. The final design presented in this thesis is based on a chiral metasurface manifesting asymmetric transmission in wide frequency band for TE polarization.
