Applications Of Electromagnetic Metasurfaces To Beam Manipulation

Electromagnetic(EM)metamaterials are artificial structures,which are composed of periodic or nonperiodic subwavelength unit cells.Due to their anomalous electromagnetic properties,metamaterials make it possible to manipulate electromagnetic waves flexibly.Electromagnetic metasurfaces are two-dimensional metamaterials,which manipulate beams by controlling the phase and amplitude of wavefront,providing cost-effective solutions to overcome bulk size,complicated design strategy,high loss and narrow bandwidth from metamaterials.More and more investigations on metasurfaces have been reported.This thesis will focus on the applications of electromagnetic metasurfaces to EM beam manipulation.The main contents and innovations are illustrated as follows:Firstly,we propose a method to control the amplitude distribution of the horn aperture using a metasurface lens.In order to suppress sidelobe levels of conventional pyramidal horn antennas in the E planes,we propose two kinds of metasurface lens,which can be placed inside the commercial standard pyramidal horn to change the uniform field distribution to be a tapered distribution over the horn aperture.The low sidelobe pyramidal horn is successfully achieved without increasing its size.Both simulated and measured results demonstrate that: the sidelobe levels have been suppressed effectively in the E planes and they are under-45 dB at the center frequency(12 GHz).Secondly,we propose a metasurface to control the polarizaion.In order to overcome the disadvantage of feed blockage and high profile in flat reflectarray antennas,we present a folded reflectarray antenna,which is composed of a linearly polarized feed antenna,a main reflector(reflectarray)and a sub-reflector(polarizing grid).The polarization converter metasurface element is able to not only twist the polarization by 90° but also provide the sufficient continuous phase compensation at the same time.The optical path in the array is folded many times,which makes the whole antenna system lower-profile.The feed blockage problem will not exist due to the integration of the feed with the reflectarray.A peak gain of 27.3 dBi and a 3-dB gain bandwidth of 27.7–31 GHz have been achieved in measurements.These results demonstrate that the antenna exhibits broad bandwidth and high gain performance.Finally,by integrating active devices with metasurfaces,the electromagnetic waves can be manipulated electronically.In order to simplify the feed network and reduce the cost of the conventional phased array,a 1-bit electronically reconfigurable metasurface element has been proposed,which is based on PIN diodes and able to generate two reflective states with a 180° reflective phase difference and a reflection loss of < 1 dB.The DC control circuit based on field-programmable gate array(FPGA)was designed and a 14 × 14 electronically reconfigurable reflectarray for beam scanning are developed.The experiment validates the simulated results.Scanning beams from-30° to +60° in the XOZ plane and-60° to +60° in the YOZ plane are achieved in the designated plane,with a peak gain of 19.2 dBi and a peak aperture efficiency of 22.53%.