Research On Broadband MIMO Antennas

In recent years,with the rapid development of 5G wireless communication systems,the demand for the capacity and reliability of mobile communication networks is increasing.However,the conventional communication technologies are difficult to solve this problem,while brings unprecedented challenges for antenna design of base station and mobile terminal.The design of antenna is usually hard to balance with each other in terms of small size and wide band,multiple antenna and high isolation.With the advent of 5G communication systems,the conventional antennas cannot meet the corresponding requirements,so we need to study the miniaturization and broadband issues of mobile terminal antennas,as well as the decoupling of MIMO antennas.Without sacrificing additional spectrum or transmitted power in rich multi-path environments,MIMO?Multiple-Input Multiple-Output?technology,which has potentiality of increasing channel capacity and improving the quality of mobile communication systems,so there is much concern in 5G communication systems.This dissertation applies to compact broadband/multi-frequency MIMO mobile phone antennas and base station filter antennas.The bandwidth of antenna is increased by exciting multiple resonant modes of the monopole and parasitic strips.By using the concept of filter to design the base station filter antenna,the isolation between the receiving antenna and the transmitting antenna of the base station antenna array can be realized.Taking advantage of the structure characteristics between the two antenna elements,the high isolation can be achieved without adding any decoupling structure.The main contribution of the dissertation can be summarized as follows:1.A compact wideband monopole for LTE mobile phone is presented.The antenna is mainly composed of a T-shaped monopole and a coupled parasitic ground strip which are excited to cover LTE800/GSM850/GSM900 bands.Moreover,three modes of parasitic ground strip contribute to covering the DCS/PCS/UMTS/LTE2300/LTE2500 bands.The merit of the proposed antenna is to cover eight bands in the 2G/3G/4G bands without any lumped-element matching circuit under the condition of limited area for antenna design,which is suitable for the wideband LTE mobile phone applications.2.A compact decoupled dual-band MIMO antennas for smartphone applications has been proposed and studied.Based on the self-decoupling structure,the compact dual-band decoupled MIMO antennas for mobile phone is realized using the structural characteristics between the two antennas.It can cover the 3.5/4.8GHz operating bands,the transmission coefficient S₁₂ is about-12 to-25 d B in the 3.5 GHz band and about-18 to-27 d B in the 5.8 GHz band.3.A single-band 4×4 MIMO antennas for mobile phone is designed.The element of the MIMO antennas is mainly composed of an L-shaped feeding strip and a coupled parasitic ground strip.Compared with the method of feeder and parasitic unit in the same layer,the layered feeding method can further improve the isolation between the elements.The MIMO antennas operate at 4.4-5GHz band,and the isolation within operating band of the antenna is greater than 20d B.4.A broadband dual-polarized antenna with second-order band-notched characteristics is designed in this letter for base station applications.The proposed antenna consists of three parts:main radiator,feed structures,and reflector.By arranging a short-ended half-wavelength U-sharped stubs next to the feeding lines and slitting the short-ended half-wavelength split-ring slots on the main radiators,a second-order notched band is achieved.The simulated results show that it has a bandwidth of 54.3%along with a sharp notch band from 1.8 to 1.93 GHz.