| Due to their high data rates and high spectrum efficiencies,diversity and multipleinput multiple-output(MIMO)technology have attracted much attention in industry and academia.Just by increasing the numbers of antennas at the end of the wireless link,the diversity/MIMO technologies can improve channel capacity and data throughput without additional spectrums or transmitting power.However,the envelope correlation coefficients between antenna elements are always very high because of the limited space of mobile terminals.Consequently,the total efficiencies of the antenna system would be correspondingly degraded.In particular,adding metal borders as the edge condition in the smartphone is currently required.To address the problem of antenna designing in a smartphone loaded with metal frames,the solutions are presented: firstly,the influence of the metal frame on an antenna system is analyzed and some design ideas are put forward in this paper;secondly,some current technologies of the single element antenna are analyzed in detail;thirdly,some antenna designs with metal frames from home and abroad are introduced briefly;finally,three kinds of metal boundary smartphone antenna systems are presented based on the aforementioned knowledge and technologies.On the basis of metal frames,conformed antenna elements and direct-involved radiation,the first kind of antenna is presented.This antenna system can be functioned as a 2×2 MIMO in the GSM850/900 band and a 4×4 MIMO in the DCS/PCS/UMTS/LTE2300/2500 band.This antenna system is formed by different types of antennas,which brings better isolations and diversity performance to the antenna system.The second antenna is presented based on the design concept of dividing the metal frame into three parts and each of them are shorted to the ground.This antenna is formed by slot antenna and the frequency reconfigurable technology is adopted.This antenna system can be used as a 2×2 MIMO in the 824~960 MHz band when the PIN diode is turned to the state 1 and can be used as a 4×4 MIMO in the 1710~2690 MHz band when the PIN diode is on the state 2.By combining the slot antenna with metal frames the influence of the metal boundary on the antenna system can be effectively reduced.The third antenna is proposed by utilizing the protruded ground between the two antenna elements to reduce the coupling and the metal frame conformed to the antenna element.This antenna system can meet the requirements of the 4×4 MIMO in the WWAN/LTE band.In particular,the analysis of the effects of the protruded ground on bandwidth broadening and isolation improvement between antenna elements is performed.The channel capacity of the antenna system with four radiating elements operating in the 824~960MHz band can reach up to 18 bps / Hz and in the 1710~2690MHz band is up to 20 bps / Hz.In this paper,three kinds of metal boundary processing schemes are closely investigated.In these schemes,the antenna systems with metal frames can function well. |
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