Metasurfaces and Their Applications in Polarization Conversion and CP Antennas

Metamaterials (MMs) are artificial media exhibiting special properties that are not found in natural materials. Metasurfaces (MSs), as a type of two-dimensional metamaterials, have the advantages of low profile, low loss, easy fabrication and integration into devices, etc. They have received a huge attention in physics and engineering over the last decades. The thesis will focus on MSs and their applications in polarization conversion, low-RCS CP antennas and dual-band CP antennas design.

For the first aspect, two topologies of reflective polarization converters are proposed. The operation mechanism is studied and a numerical analysis is performed. 1) A broadband and high-efficient polarization converter is proposed. The polarization converter can convert a linearly polarized (LP) incident EM wave (x/y-polarized) into a cross-polarized reflected wave (y/x-polarized). 2) A triple-band and high-efficient multi-functional polarization converter is proposed. The proposed design can convert an LP incident electromagnetic (EM) wave into a cross-polarized reflected wave in the first and third band and a circularly polarized (CP) reflected wave in the second band, respectively.

For the second aspect, owing to the polarization conversion characteristic of MSs, a low-RCS and high-gain CP array are proposed. First, a mushroom-type MS-based superstrate is designed and integrated with a traditional LP slot antenna. Second, an array is developed by using four element antennas and a sequentially rotated feeding network. Concerning radiation, the array has a wideband and high gain. Concerning scattering, the array achieves RCS reduction in both in-band and partially out-of-band.

Besides, a novel wideband checkerboard-like method for RCS reduction is proposed and applied in CP antennas. The technique is based on an MS and a grounded substrate. The broadband RCS reduction is achieved by combining two different destructive interference principles. Besides, the MS can be applied in traditional CP patch antennas. It achieves a significant bandwidth and gain improvement as well as broadband RCS reduction.

For the third aspect, the surface wave propagation of MSs has been analyzed and applied in CP antenna design. A dual-band CP antenna is designed by the combination of an MS-based superstrate and a traditional CP patch antenna.

All the designs have been fabricated and measured. The measurements and simulations are in good agreement.