Applications of metasurfaces in antennas design

Abstract

This thesis presents the applications of metasurface (MS) in the design of reconfigurable antennas, small MS lens antenna, miniaturized patch antenna and dual-band slot antenna, all implemented using planar technology.

A MS is proposed to convert a linearly polarized (LP) antenna to a circularly polarized (CP) antenna. The MS is placed atop a patch or slot antenna, denoted as the source antenna in this arrangement. Based on this, MS is further used to design three reconfiguration antennas, namely, a polarization-reconfigurable antenna MS (PRMS) antenna, frequency-reconfigurable MS (FRMS) and mechanically patter-reconfiguration MS (PaRMS) antenna.

The PRMS antenna is composed of a slot antenna with a MS placed atop of and in direct contact with it. Both MS and source antenna have a circular shape with same diameter. By rotating the MS around the center relative to the slot antenna, the PRMS antenna can be reconfigured to LP, left-handed (LH) and right-handed CP. The FRMS antenna again consists of a MS and patch antenna with circular shape of same diameter. By rotating the MS around the center relative to the patch antenna, the operating frequency of the antenna can be tuned. A measured tuning range from 4.76 to 5.51 GHz (14.6%) is achieved. The FRMS antenna is improved by replacing the patch antenna with a slot antenna and using a better design of unit cells on the MS. Results show that the FRMS has a much wider tuning range of 28% (from 2.64 to 3.5 GHz). Analyses show that, in such arrangement, the MS behaves like a dielectric substrate. Rotating the MS alters the effective-relative permittivity of the substrate and hence the operating frequencyof the FRMS antenna, resulting in frequency reconfiguration. The mechanically PaRMS antenna is composed of a planar semi-circular MS placed directly atop a circular patch antenna. The main-beam direction has an angle of 32°from the boresight direction of the patch antenna, which can be steered continuously by rotating the MS around the center of the patch antenna.

In the small lens antenna, a small MS lens is placed in front of a source antenna, a slot or patch antennas, to enhance the boresight gain. The unit cells on the MS has rectangular-loop shapes, with a constant width along the horizontal direction and varying lengths following the gradient index (GRIN) function along the vertical direction. Results show that the small MS lens can effectively reduce the main beamwidths and enhance the boresight gains of the source antennas.

In the miniaturized patch antenna, the MS is placed atop and in direct contact with a patch antenna. Results show that, the MS can reduce the size of the patch antenna by 67% with any performance degradation.

In the dual band CPW-fed slot antenna, the MS is on the other side of the slot. Results show that the two operating bands ataround3.4 GHz and 5 GHz are generated, with the unidirectional radiation patterns pointing to the opposite directions.