| Since the concept of the Internet of Things was proposed and vigorously promoted at the end of the 20 th century,wireless communication technology and its applications have once again set off an upsurge in the world.2.4 GHz is a universal wireless working frequency band,and its related product development and application in the Internet of Things system have been rapidly developed.The antenna is a key part of the wireless signal transceiver,and the performance of the antenna directly determines the overall working capability of the transceiver system.The development demand for miniaturization of wireless systems has pushed the miniaturization of antennas and the expansion of the number of channels to current research hotspots.The research and development of antenna miniaturization technology and Multiple-Input Multiple-Output(MIMO)technology is very important in mobile terminal applications.Multifunctional and miniaturized terminal antennas are one of the research focuses of this article,including small The research of dual-frequency reconfigurable antenna and miniaturized MIMO antenna.Indoor micro base stations have higher requirements for wide beam coverage and circular polarization.The omnidirectional circular polarization technology as a key technology of micro-unit antennas has become another research focus of this article.This article focuses on the miniaturized dual-frequency technology,multiple input multiple output technology,and omni-directional circular polarization technology in the key technology of 2.4 GHz antenna applied to the Internet of Things system.The first is the research on the 2.4 GHz miniaturized dual-band antenna in the Internet of Things system.In order to realize the dual-frequency radiation and miniaturization design of the antenna,this work adopts the capacitive loading method on the basis of the monopole single-frequency antenna,which not only ensures that the original high-frequency radiation is almost unchanged,but also introduces low-frequency radiation.At the same time,due to the introduction of the loading structure,the overall design of the antenna is more compact and the size is further reduced.In order to achieve the frequency adjustable characteristics of the antenna in the 2.4 GHz frequency band,this design introduces a tunable capacitor.Due to the low-pass and high-impedance characteristics of the capacitor,the antenna realizes the low-frequency frequency adjustable function under the premise of the same high frequency and radiation.The second is the research on the 2.4 GHz miniaturized MIMO antenna in the Internet of Things system.On the basis of the research of miniaturized unit loaded antennas,this article then analyzes the mutual coupling between multiple antennas in the MIMO system,introduces a method for achieving high isolation between antennas in odd and even modes,and proposes an application to the Internet of Things The mobile terminal 2.4 GHz in the system is a novel MIMO antenna design based on the parity mode analysis method.First,in order to achieve higher antenna isolation,this thesis proposes a dual-element antenna with directional pattern/polarization diversity characteristics based on odd and even mode feeding.On the basis of this feed structure,the dual-port radiation of the antenna realizes a co-aperture design,which improves the efficiency of space use,the overall size of MIMO antenna is further reduced.The last is the research on the 2.4 GHz miniaturized indoor micro base station omni-directional circularly polarized antenna in the Internet of Things system.First,the basic theory of the composite left-handed transmission line and the negative permeability metamaterial transmission line are introduced.Then,in order to realize the omnidirectional circular polarization radiation characteristics of the antenna,a model of a vertical monopole and a horizontal in-phase current loop is adopted.Through the measure of short circuit inductance loading around,the cross-sectional size of the antenna is reduced a lot.The vertically polarized omnidirectional mode is resonated from the zero-order mode of the center-fed mushroom-type composite left and right-handed transmission line.The horizontally polarized omnidirectional radiation is caused by the capacitively loaded transmission line around,that is,the zero-order of the negative permeability transmission line.There is a natural 90-degree phase difference between the two polarizations,and finally an omnidirectional circularly polarized antenna with a low profile is obtained.The working frequency band of the omnidirectional circularly polarized antenna used in micro base stations proposed in this thesis covers 2.3 GHz-2.6 GHz,and the circularly polarized bandwidth basically covers the commonly used 2.4 GHz ISM bandwidth requirements. |
PDF Full Text Request