A Multiband Dual-Antenna System With a Folded Fork-Shaped Ground Branch and Folded Asymmetric U-Shaped Slots for Smartphone Applications

A multiband dual-antenna system for smartphones operating at LTE700/2300/2500/3400, GSM850/900, DCS, PCS, UMTS, 2.4-GHz WLAN, 3.5-GHz WiMAX, and 5-GHz WLAN bands is presented and studied. The proposed dual-antenna system includes two symmetric antenna elements and a folded fork-shaped ground branch (FFGB). A driven branch and a dual-branch parasitic ground branch that makes up the antenna element generate a couples of resonant modes in the foregoing targeted bands. To reduce the mutual coupling between the two closely spaced antenna elements and improve the bandwidth, the FFGB is used. A folded asymmetric U-shaped slot is etched on each dual-branch parasitic ground branch to make the bandwidth of the dual-antenna system fully cover the 5-GHz WLAN band. The measured bandwidth of the fabricated prototype with lower than 6 dB reaches 687-980, 1709-2891, 3300-4031, and 5011-6000 MHz, covering all the targeted bands. Within the LTE700/GSM850/900 bands, the measured is lower than 10 dB. For the rest operating bands, the measured is lower than 15 dB. The envelop correlation coefficient, the mean effective gain, and the diversity gain of the proposed dual-antenna system are calculated based on the measured three-dimensional (3-D) radiation patterns, and good results are obtained.