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 |S₁₁| 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 |S₂₁| is lower than -10 dB. For the rest operating bands, the measured |S₂₁| 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.