Research On High-gain And High-focus Microwave Antenna Technology

The 6th generation mobile communaction system(6G)is an extension of 5G,which puts forward higher requirements for communication distance and communication capacity.As a key device of wireless communication system,the antenna is responsible for transmitting(Tx)and receiving(Rx)electromagnetic energy,whose performance directly affects the quality of communication.High-gain array antenna and highfocus vortex electromagnetic wave antenna carrying orbital angular momentum(OAM)play a key role in improving communication distance and channel capacity.In this thesis,high-gain and high-focus microwave antenna technology is studied.The main research contents and innovations are as follows:1.Aiming at the problems of element coupling,high microstrip line loss and high cross-polarization level of microstrip patch antennas,a dualband dual-polarized high-gain array is proposed.The coupling between elements is reduced by the structure of the metal via-loaded rings,and the gain of the antenna is improved by using low-loss substrate integrated coaxial line(SICL).The low-cross polarization level performance is achieved by using a differential feed network based on the miniaturized three-port coupler,and the broadband performance is achieved by using a multistage impedance-matching feed network.The aperture efficiency of the 4×4 array for Rx/Tx ports is 40.8%and 48.3%,respectively.The measured impedance bandwidth of the 16×24 cruciform antenna array for Rx/Tx ports is 22.1%(10.57-13.33 GHz),21.1%(12.31-15.32 GHz),respectively.The isolation of Rx and Tx ports is better than 47.5 dB in the working frequency range.The measured gain of Rx/Tx ports is greater than 26.8 dBi and 29.0 dBi respectively,and the corresponding aperture efficiency is greater than 25.0%and 30.9%.The measured crosspolarization level is better than-38.3 dB.The antenna can achieve the first sidelobe level of-15.1 dB and the scanning range of±4.5°.2.To overcome the shortcomings of narrow bandwidth and low purity of dual-feed microstrip patch OAM antenna,a broadband four-feed circular patch antenna is proposed to generate high-purity dual-mode vortex beams.A four-feed circular patch structure is designed to excite four orthogonal degenerate modes of TM21,thereby improving the mode purity and bandwidth.The measured results show that the impedance bandwidth of both ports is 44.2%(4.75-7.40 GHz)and the 3-dB axial ratio bandwidth is 28.33%(5.33-6.70 GHz).The circularly polarized(CP)gains of both ports are 5.81 dBic and 6.23 dBic,respectively.The OAM mode purity of ±2 is greater than 90%.3.Aiming at the beam divergence problem of conventional OAM beam,a non-diffracting Airy OAM wave reflectarray antenna is proposed based on the Airy-OAM-phase modulation method.To reduce the design time,a near-field synthesis technique is used to theoretically analyze the non-diffracting characteristics of the Airy OAM beam.A hexagonal dualresonance element,composed of a hexagon ring around a square patch,is employed in the reflectarray to provide a linear phase range of 360°,which is insensitive to polarization and incident angles.To verify the effectiveness of the design,the Airy OAM reflectarray with 15055 elements is fabricated and measured.The experimental results show that an Airy OAM beam with the mode of+1 is successfully generated from 44 to 49 GHz.Moreover,the measured results validate the autofocusing and self-healing properties of the Airy OAM beam.4.In order to solve the issue of unequall divergence angle for two different OAM modes,a single-layer reflectarray is proposed to generate dual-mode dual-polarized high-order Bessel vortex beams with equal divergence angle.The proposed reflectarray consists of two different subwavelength elements with different polarizations,which are located in the inner disk region and the outer ring region respectively.The inner element is composed of a square ring and a regular octagon,which is proposed to achieve a linear phase response of 360°.The outer element,which consists of a microstrip line and a double W-shaped line,is designed to achieve the phase compensation and polarization conversion simultaneously.The equal divergence angle of different OAM modes is achieved by theoretically calculating the radii of the inner and outer regions.A reflectarray prototype is fabricated and tested,and the results show that the high-order Bessel beams with+1 mode of x-polarization and+2 mode of y-polarization are successfully generated with equal divergence angle from 27-31 GHz.