Research And Applications To Antennas Of Metasurfaces With Polarization Transformation

Electromagnetic metasurfaces are two-dimensional metamaterials with advantages of lower profile,thinner thickness,more flexible,and easier designing and fabricating.In order to cope with complex environments,more and more investigations on polarization transformers have been reported,due to their advantages of the polarization diversity and simple structures.This thesis will focus on the research of metasurfaces with polarization transformstion and their applications to antennas.The main contents and innovations are described as follows:Firstly,in order to overcome the problems of complex structure,complex assembly and higher cost of conventional circularly-polarized horn antennas,we propose a transmission metasurface with the functionality of linear-to-circular polarization,which can be placed on the aperture of existing linearly-polarized standard gain horn antennas,resulting in circularly-polarized(CP)horn antennas.Both simulations and experiments show that the CP performance(3-dB axial ratio)is in the range of 28.5 GHz to 30.7 GHz,up to 7.4%,with a maximum gain reduction of 1.1 dB compared with that of the original standard pyramidal horn.The design has the advantages of simple structure,simple assembly,and low cost.As an extension,we also successfully apply this method to Ku-band standard horn,verifying its design flexibility at other frequency band.Secondly,in order to overcome the large volume or complex feed network existing in conventional high-gain antennas,a high-gain transmitarray antenna is developed.Electromagnetic metasurfaces that can provide the sufficient continuous phase compensation and high transmission efficiency are studied and developed.With the transmission phase compensation,a transmitarray antenna is designed.Simulated and experimental results show that antenna achieves a simulated peak gain of 31.68 dB,a measured peak gain of 31.38 dB,an 1-dB gain bandwidth of 13.1%,a 3-dB gain bandwidth of 26.6.%,and a maximum aperture efficiency of 45.2%.Finally,in order to further reduce the volume of the transmitarray antenna,a folded transmitarray antenna has been proposed,Since the optical path in the folded transmitarray is folded three times,the profile of the folded transmitarray antenna is about one third of the originsl transmitarray antenna.Both simulations and experiments demonstrate that a peak gain of 25.2 dB,a 3-dB gain bandwidth of 24.9-29.8 GHz,and an aperture efficiency of 13.8% are achieved.In order to improve the gain and the aperture efficiency,a integrated 2×2 microstrip patch array antenna is designed to feed the folded transmitarray.The simulated peak gain is 29.63 dB,the 1-dB gain bandwidth is from 28.1GHz to 30.5GHz,about 8.2%,and the maximum aperture efficiency becomes 30.55%.Considering multi-polarization applications,the feasibility of a circularly-polarized folded transmitarray antenna is verified.The simulations show that circularly-polarized performance achieves in the range of 27.3GHz-29.2GHz,a 3-dB axis ratio bandwidth of 6.7%.