Radiation Features Of Next-generation Mobile Antennas And Broadband Circularly-polarized Antenna Design

In the past half a century,mobile communication becomes an indispensable technology in people's daily life.The new applications,such as virtual reality,pilotless automobile,and Internet of Things,demand for higher data rates and greater channel capacity.In this context,the research about the fifth-generation(5G)communication technologies is carried out globally.As one of the key components and technologies,antennas play a vital role.The purpose of this paper is to explore the electromagnetic-field exposure of millimeter-wave antennas implemented in 5G user equipment,the effects of realistic user equipment on the antenna performance,and circularly-polarized antenna deisign for broadband wireless communications.The main academic contributions are summarized as follows.1.28 GHz user equipment mock-ups utilizing patch arrays,notch arrays,and slot arrays are designed separately.Using full-wave simulation software and numerical calculation,it is found that the excited surface waves increase the radiation aperture and then decrease the.maximum power density levels.Based on the FCC,ICNIRP,and IEEE safety guidelines,the mamxium permissible transmitted power of the mock-ups are 0.5 dBm-16.4 dBm,far below the transmitted power levels of user equipment in current cellular bands(23 dBm-33 dBm).2.Based on the equivalent power density and the combination principle of antenna arrays,various power density assessment methods are proposed,including the scalar field combining methods and the vector field combining method.The electric fields produced by 15 GHz user equipment mock-ups are measured using the near-field measurement system.The advantages and disadvantages of different assessment methods are given.3.Using the eigenvalue decomposition and the semi-definite relaxation,the strict upper bounds are given for the power density of millimeter-wave antenna arrays.The methods are used for the upper bound calculation of a 28 GHz notch array,and are verified by the Monte Carlo method.The maximum permissible transmitted power levels are given according to the relevant safety guidelines.4.Using full-wave simulation softwares and a near-field measurement system based on an inverse source technique,the effects of chassis,casing,displays,scattering and user's hands on 28 GHz antenna performance are systematically analyzed.The effective beam-scanning efficiency is proposed to account for the aforemetioned effects on the beam-scanning capability.Various structures are designed to suppress the surface waves on the chassis to improve the antenna patterns.5.Two types of broadband circularly-polarized wide slot antennas are designed.Based on the classic wide-slot antenna designs,introducing the protruding ground structure leads to a 58%axial-ratio bandwidth.The same design principle is applied to the handheld broadband RFID reader antenna.The antenna has a smaller dimension,and in the meanwhile it can cover the universal Ultra-High Frequency RFID bands.