Research Of Millimeter-wave Wideband Circularly-polarized Antenna Element And Array

With the development of wireless communication technologies,millimeter-wave wireless systems have received extensive attention due to their large bandwidth and high transmission rate.Millimeter-wave wireless systems have important potential applications in the fields of satellite communications,the fifth-generation mobile communications,and autonomous driving.As an important component of the millimeter-wave wireless systems,millimeter-wave antenna could affect the performance of the entire system,which makes the development of broadband millimeter-wave antennas of high academic and application value.In this dissertation,a series of investigations is carried out on the design,optimization,and experimental verification of millimeter-wave broadband circularly-polarized antenna elements and their sequential rotation arrays.It mainly includes the following three parts:The first part proposes and verifies a Ka-band compact broadband circularly-polarized antenna based on artificial ground structures and its sequential rotation array.The antenna element utilizes the double resonances provided by the compact artificial ground structure and the truncated patch to generate broadband circularly-polarized radiation.In addition,based on the element design,a 2 × 2 element sequential rotation array is designed to further improve the circularly-polarization bandwidth.The sequential rotation array is fabricated and experimentally verified,achieving a-10 d B impedance bandwidth of 28.7% and a 3d B axial ratio bandwidth of 27.2%.In the second part,a K-band wideband circularly-polarized antenna element based on stacked patches with slot cuts and its sequential rotation array are developed.The antenna element is composed of a microstrip slot-coupled feeding structure,a main driving patch,and a parasitic patch.The two patches of different sizes couple with each other,thereby realizing broadband circularly-polarized radiation.Based on the element design,a 2 × 2 element sequential rotation array is developed to further extend the circular polarization bandwidth.In addition,a more compact feed network is designed.The array is experimentally validated,showing a measured 3d B axial ratio bandwidth of 25.7%,within which the S11 is less than-10 d B.In the third part,the genetic algorithm is used to optimize the pattern characteristics of random sequential rotation arrays for achieving low sidelobe and high circular-polarization purity.Firstly,the formula for calculating the pattern of an equally spaced array composed of rotating elements is given,which is evaluated by considering an array of stacked-patch broadband circularly-polarized antenna elements.On this basis,genetic algorithm and pattern synthesis method are jointly utilized to optimize the element feeding phase and element rotation angle distributions of random sequential rotation arrays,both at a single frequency and within a wide bandwidth.The impacts of degree-of-freedom of different random sequential rotation schemes on the cross-polarization level,side-lobe level,and gain are compared and analyzed.Finally,the calculated results of the optimized array and the simulation results are compared and analyzed,and the feasibility of the proposed design method is verified numerically.It shows that the optimized random sequential rotation array can simultaneously obtain smaller side lobes and a lower cross-polarization level,which provides new ideas for the design of broadband low-sidelobe circularly-polarized antenna arrays.