Research Of Wideband High Gain Circularly Polarized Antenna Based On Polarization Conversion Metasurface

Polarization is one of the fundamental properties of electromagnetic waves(EM).With the rapid development of communication technology,controlling the polarization performance of electromagnetic waves is of great significance for microwave and millimeter wave communication.The electromagnetic wave is converted from linear polarization to circular polarization using metasurface.The application is needed in advanced communication and sensing systems because the circular polarization(CP)electromagnetic wave is more sensitive to reflection than linear polarization(LP)electromagnetic wave.Circularly polarized(CP)antennas have become the most popular because of numerous advantages,including avoidance of multipath effects,good resistance to polarization mismatch,immunity to Faraday rotation,and some phasing issues.However,the bandwidth and gain of circularly polarized antennas need to be further improved.The broad bandwidth is rendered possible through the unit cell’s distinctive structure,which creates several electric and magnetic resonances in the required frequency range.The metasurface(MS)has been currently used to enhance the gain of circularly polarized antennas.This thesis conducts research based on a linear to circular(LTC)polarization conversion unit cell of the metasurface and broadband high gain circularly polarized antenna.In this dissertation,a circularly polarized(CP)antenna based on polarization conversion metasurface(PCMS)is analyzed and designed to meet the growing requirements for wideband high gain antennas.The following are the major contributions of this work:1.A novel three-quarter circular-shaped metasurface unit cell embedded in a rectangular patch with a wide axial ratio bandwidth(ARBW)and high ellipticity is proposed,which converts LP-incident waves into right and left-hand circularly polarized waves(RHCP and LHCP)in a single frequency band.According to the principle of linear to circular polarization conversion,the rectangular slot etched on the rectangular patch embedded with a quarter circular-shaped metasurface can convert a single broadband into a dual frequency band.A single and dual wideband circularly polarized reflected wave is achieved under an incident wave polarized along the y-direction.The single wideband circularly polarized achieved ARBW of 50.8%in the frequency band of 20.18GHz-33.93 GHz.Also,dual wideband circularly polarized achieved ARBW of 35.23%and 26.62%in the frequency band of 16.49 GHz-23.54 GHz,and 26.44 GHz-34.56 GHz.The polarization conversion ratio(PCR)of single and dual bands exists above 98%.A theoretical study is described to comprehensively understand the fundamental root of the linear to circular polarization conversion when the Δφuv between two reflection coefficients at u and v-polarized incidences is±90° or an integral multiple of±90°,which fully determines the reflected wave ARBW.2.A novel high-gain circularly polarized antenna is proposed based on parallel rectangular patches MS.The proposed antenna is composed of a three-layer substrate with a 1 × 11 array of parallel rectangular MS patches integrated on the upper substrate and a rectangular slot etched on the ground plane.The frequency range of the proposed antenna is 614 GHz.The proposed antenna array was fabricated and measured with the overall size of 12 mm × 12 mm × 3.54 mm(～0.4λ0 × 0.4 λ0 × 0.119λ0)at center frequency of 10 GHz.The measured and simulated results showed that the CP antenna achieves good performance with IBW of 95-10.68 GHz(17.63%)and axial ratio(AR<3 dB)bandwidth of 10.62-11.87 GHz(11.12%).Moreover,the MS-based antenna array achieved a high gain of 6.5 dBic at 13.60 GHz.3.A novel low-profile wideband circularly polarized(CP)antenna based on a rectangular patches-shaped MS array(2 × 2)is proposed.A power divider(sequentially phase network)activates each radiating unit using phase distributions of 0°,90°,180°,and 270°,which can be used to produce circularly polarized radiation.The proposed antenna array(2 × 2)was fabricated and measured with an overall size of 40 mm × 40 mm ×3.58 mm(～1.2 λ0 × 1.2 λ0 × 0.106 λ0)at 9.0 GHz.The simulated and measured results show that the proposed antenna has a-10dB IBW of 30.89%(7.80-10.65 GHz)and 3 dB axial ratio bandwidth of 16.90%(9.05-10.72 GHz).Moreover,the metasurface-based antenna array produced broadside circularly polarized radiation of more than 90%within the AR bandwidth with a peak gain of 7.2 dBic at 11.29 GHz.4.A new three-quarter circular-shaped metasurface design is proposed.The proposed design improves the CP’s broadside gain and impedance bandwidth.It happens due to minimum insertion loss using a rectangular slot with a microstrip-fed line based on a dual-layer dielectric substrate.A microstrip line is introduced at the bottom of the MS-based antenna through a feeding network slot etched on the ground plane,constituted by an 4 × 4 array of three-quarter circular-shaped MS patches.A novel proposed CP slot antenna array was designed and measured with an overall size of 50 mm × 50 mm × 2.33mm(～1.59 λ0 ×1.59 λ0 × 0.07λ0)with the aim of the IBW and gain enhancement.The IBW is 25.82%from 8.6 to 11.15 GHz,3dB ARBW is 12.42%covers from 9.89 to 11.20 GHz,and has a peak gain of 9.52 dBic with good CP at an operating frequency of 11.20 GHz.