Tunable antenna for mobile applications

Abstract

A frequency tuned antenna working in several LTE frequency bands is proposed and modelled. The double PIFA-type antenna, containing low and high frequency branches is placed on the back cover of a handset. A varactor diode is used for antenna tuning. The varactor is connected to the middle of the low frequency antenna branch. Simulation by RFS computer code shows that antenna can be tuned to one of four LTE low frequency bands keeping tuning to the high frequency band by changing varactor bias from -1 to -8.5 V, which corresponds to changing varactor capacity from 5 to 1.35 pF. Antenna radiation efficiency varies from 25 to 52 % in low frequency bands and rises up to 70 % in high frequency band. Relative bandwidth of the antenna in low frequency bands varies from 6.6 to 10.2 % and is 9.4 % in high frequency band.