Planar Circularly Polarized Antennas And Arrays For Millimeter-wave Wireless Applications

The ever growing traffic explosion in wireless mobile communications has recently drawn much attention to the wide bandwidth in the millimeter-wave(mmWave)frequency band,in the demand for the 5th-generation mobile communications(5G).The dissertation focuses on the design and optimization methods of the planar circular polarization(CP)antennas and antenna arrays operating at mmWave band.The dissertation is organized as follows:First,a brief review of the mmWave systems for wireless communication applications and the associated frequency spectrum allocation is proposed.The research status of the topics including design strategies for the planar antennas,the cavity backed slot antennas(CBSAs)and the CP antennas,and the optimization methods for electromagnetic component designs is introduced.The research contents and objectives in the dissertation are described.Second,a series of Substrate Integrated Waveguide(SIW)-like cavity based CBSAs is proposed.Based on the equivalent method between the SIW and the Half-Mode SIW(HMSIW)cavity,using the integration and disintegration processes of the cavities,the miniaturization and the bandwidth enhancement design methods are proposed.An HMSIW CBS antenna is designed with measured impedance bandwidth of 12.1%,3 dB axial ratio(AR)bandwidth of 2.3%and peak gain of 5.3 dBic using almost half the size of the corresponding SIW CBSA design.Then,a dual-band broadside radiation CP SIW CBSA is designed at both 37.5 GHz and 47.8GHz.Last,a broadband SIW CBSA is proposed with measured impedance bandwidth of 21.3%,radiation efficiency higher than 84.7% and peak gain of 5.72 dBi.Third,an antenna array for mmWave broadband CP applications is proposed.An 8 × 8 antenna array with broadside broadband CP radiation is designed.Using stacked curl structure,the broadband CP antenna element is designed with travelling wave performance.The broadband full-parallel feeding network and the boundary conditions of the element are designed and investigated,respectively.The designed array achieves measured impedance bandwidth of35.4%,3 dB AR bandwidth of 33.8% and peak gain of 23.5 dBic.Fourth,a low-profile wideband multi-beam end-fire dual CP antenna array is proposed.Based on the dielectric-loaded stepped slot SIW end-fire antenna element,the SIW beam-forming feeding network,interconnections and transitions,a broadband multi-beam end-fire dual CP antenna array is firstly achieved.The designed array achieves measured overall bandwidth of22.5%.Fifth,a series of machine-learning assisted optimization methods is proposed.Using the surrogate models constructed by the machine-learning method,several above mentioned antenna prototypes are optimized by the proposed novel optimization algorithms.First,two machine-learning-assisted single-objective optimization methods(MLSOOMs)are proposed to optimize the designed broadband SIW CBS antenna operating at mmWave band and the end-fire CP antenna element.The quad-mode broadband SIW CBSA achieves measured impedance bandwidth of 23.7%.Second,two machine-learning-assisted multi-objective optimization methods(MLMOOMs)are proposed to optimize the designed CP SIW CBS antenna and the CP travelling wave antenna element.Investigations on the view addition of the training set,the affection of the utilization of the uncertainty and the introduction of the complete optimization process are proposed.