Researchand Design Of Frequency Tunable Antennas For Mobile Terminals

With the development of mobile communication technology,it's the trend for mobile terminals to supply multiple functions and support multi-standard communication networks.As one of the most important components of mobile terminals,antennas can directly impact the performance of the mobile communication system.With the increasing demand for ultra-thin smart terminals,the available space for designing the required antenna is limited,which leadsto narrower working bands and lower efficiency.Frequency tunable antenna is one of the practical solutions to support multiple bands within limited space.By integrating RF tunable components into antenna design,tunable antenna can obtain wide frequency coverage by combining various working states of the RF components.This paper mainly focuses on the research of frequency tunable antennas for small-size and multi-band mobile terminals.Two types of tunable techniques have been studied,namely,tunable impedance matching and tunable aperture.Firstly,a small-size tunable antenna with a tunable impedance matching circuit for ultra-thin smartphone application has been proposed.The proposed antenna has a simple structure and a compact volume of 45×4.5×2 mm~3,which is formed by a folded monopole as main radiation branch and a small stub as tuning branch.The matching network can be switched by employing only one PIN diode.By combining the two working states of the PIN diode,the proposed antenna can cover GSM850/GSM900/DCS1800/PCS1900/UMTS2100,andtwoLTEbands LTE700/LTE2300.As the height of proposed antenna is only 2 mm,it is therefore a good candidate for slim smart phone antenna design.Then,a small-size aperture tunable antenna for mobile application has been successfully demonstrated.The proposed antenna has a compact volume of 55×5×3mm~3.It consists of a folded loop structure,two tuning branches and an RF switch.In addition to the traditional three loop antenna modes,namely,0.5-?,1-?and1.5-?modes,the proposed loop antenna also generates another 2-?mode.An RF switch is applied to improve the operating bandwidth with four working states.By combining the four working states of the RF switch,the proposed antenna can cover GSM850/GSM900/DCS1800/PCS1900/UMTS2100/LTE2300/LTE2500 bands.The average efficiency is over 50%at low band and 52%at high band.Based on the desirable antenna performances with broadband coverage,high efficiency and low SAR,the proposed antenna is a good candidate for slim smart phone applications.