| Recently,with the rapid revolutions of the technologies of wireless communications and internet,they strongly drive the developments of the whole consumer electronics of wireless communications.More and more wireless devices have entered people's daily life and work,which leads human to acquire information resource in a convenient and efficient way.As the front port of the entire wireless communication system,antenna is responsible for transmitting and receiving the radio signal,and its performance influences the quality of the wireless communications in a great extent.With the growing of users' requirements and the developments of the corresponding technologies,as for the wireless communication devices,the integration level becomes higher and the functions become more complicated.Therefore,this situation urgently compels the antennas to decrease their own dimensions as small as possible and guarantee the high communication quality at the same time.Besides,modern communication devices are required to transmit high-rate and mass information,and sometimes they are even requested to obtain multiple communication modes.Then,antenna systems should be able to support wider operation bandwidth and possess multi-working modes simultaneously.Consequently,studies about wide and multiple bandwidths for antenna system are extremely important.On the other hand,for communications,the inevitable refractions and reflections exist in the electromagnetic wave's propagation,which leads to the multipath fading for the receiver.Multiple-Input-Multiple-Output(MIMO)technology adopts multiple transmission antennas and multiple receiving antennas.It enhances the reliability and capacity of the communication system channel and increases the transmission efficiency.Compared to the linearly polarized antennas,circularly polarized(CP)antennas possess good anti-interference capability,low polarization mismatching and other some advantages.Thus,they are widely employed in modern wireless communication systems as well.Revolving around the aforementioned topics,this thesis will primarily present the studies in two aspects.For the first aspect,it begins with the studies about the applications of MIMO technology in Ultra-Wideband(UWB)antenna,and then conducts the researches and analyses about the decoupling between antenna elements and the realization of polarization diversity.For the second aspect,the thesis will show the researches about the applications of magnetoelectric(ME)dipole antenna in wide band and multiple bands.And the circularly polarized features will be introduced into the design of ME dipole antenna.The main working contents of this thesis are given bellow.(1).This thesis illustrates the developments and research backgrounds of the UWB,MIMO,wideband and multi-band technologies.Revolving around the topic of the thesis,it will state the overseas and domestic research actuality and developing status of the UWB MIMO and ME dipole antennas.The examples and analyses will be presented as well.Meanwhile,the thesis will emphatically discuss and summarize about the decoupling mechanism,complementary theory and antenna polarization theory.This will lay the theoretical foundation for the later contents.(2).UWB antenna with half-slot structure.In this part,a UWB antenna with metamaterial unit loading is proposed at the begining.This antenna obtains the zero-resonant mode via employing the left-hand inductor.By merging the bandwidths of zero-resonant mode with other resonant modes,the proposed UWB antenna can completely cover the upper band of the UWB communication(6-10.6 GHz).Based on the above studies,a UWB MIMO antenna with half-slot structure is proposed,and the operation mechanisms of the half-slot structure are analyzed and explained in detail.This proposed UWB MIMO antenna possesses extremely compact structure and it also realizes superior decoupling performance and far-field characteristics.Otherwise,the measurements errors resulting from the outer connected cable will also be explained specifically in the thesis.(3)UWB MIMO antenna with filtering features.Firstly,a compact UWB MIMO antenna with high isolation is proposed.By notching a fork shaped slot on the ground plane,the isolation of two antenna elements is improved in a large margin.Then,two quarter-wavelength open-ended slots are introduced on the radiators,leading to the notch band over the WLAN frequency range.It can be discovered through previous studies,single filter structure only generates one single resonant frequency and the realized notched band decreases sharply along two sides of the centre frequency.This may cause the problems of effective bandwidth narrowing and filtering performance deteriorating around the cut-off frequencies.Thus,a UWB MIMO antenna possessing four different filter structures is proposed without increasing the whole dimensions of the antenna.Within the interference frequency range,the proposed antenna realizes relatively stable stop bands and sharp declines around the cut-off frequencies.The antenna adopts embedded design idea.The antenna element with small size is designed integrated into the larger one,which realizes compact structure and antenna miniaturization.(4)Wideband,multi-band ME dipole antenna.First of all,a substrate-printed director is added to the ME dipole antenna,which efficiently offsets the gain declines at the higher frequencies.Adding the director also introduces some advantages of Yagi antenna to the original antenna,such as enhancement of front-to-back ratio,improvements of peak gain,and so on.By tuning some parameters of the antenna properly,the proposed antenna will realize a wide operation bandwidth and the variation of the peak gain is almost constant within the frequency range.A dual-band,wideband ME dipole antenna loading the similar director structure is proposed later.The director in this antenna is designed in full-metal material,and it helps to widen the operation bandwidth at lower frequency.The parasitic element is designed beneath the original electric dipole element,which reduces the whole antenna profile and prevents the radiation patterns from distortions at higher frequencies simultaneously.(5)Dual-band,dual-sense CP ME dipole antennaIn this thesis,the guidance of how to realize the circular polarization in ME dipole antenna is presented in detail,and a wideband CP ME dipole antenna is designed to verify the above guidance.Then,based on these studies,the ME dipole antenna with dual-band,dual-sense circularly polarized features is proposed firstly in the thesis.The antenna is combined with two ME dipole antenna elements with different dimensions.A crossed ?-shape feeding line is introduced to excite separate elements and then it allows the proposed antenna to realize wide operation bands.Finally,the antenna achieves right-hand circular polarization and left-hand circular polarization at its higher and lower operation bands,respectively.It also possesses good directional radiating performance and high radiation gain and efficiency. |
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