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The metal‐frame long‐term evolution (LTE) antennas with a compact symmetric frame structure at the short edge of the metal‐framed smartphone are presented. The proposed metal‐frame antennas cover the LTE low band (LB) in 824~960 MHz and two LTE middle/high bands (M/HBs) in 1710~2690 MHz. The LTE LB antenna uses a short metal‐frame section of 41.8 mm (about 0.12 wavelength at 824 MHz). The two LTE M/HB antennas together use a continuous metal‐frame section of 41.8 mm (about 0.24 wavelength at 1710 MHz), same as the LTE LB antenna. The two LTE M/HB antennas show low envelope correlation coefficient (ECC) of <0.1 in 1710~2690 MHz, owing to using a capacitor‐loaded shorting strip for the two antennas conjoined to achieve a compact and decoupled structure. The low ECC allows the two LTE M/HB antennas to be promising for 2 × 2 multi‐input multi‐output operation.

A printed dual‐feed U‐shaped open‐slot (U‐slot) antenna disposed close to the top or bottom short edge of the system ground plane in the metal‐framed smartphone for the LTE (long‐term evolution) MIMO (multi‐input multi‐output) operation is presented. The U‐slot is printed in the ground region within 10 mm to the short edge of the system ground plane and its two open ends are disposed at the short edge thereof. The former makes the system ground plane capable of accommodating a large display panel for the smartphone, while the latter decreases the effects of the user's hand holding the smartphone. The U‐slot is short‐circuited at one position therein to provide one longer open slot and one shorter open slot, which are fed separately by two feed networks to form Ant1 and Ant2. Ant1 can cover the LTE low band (LB, 746–960 MHz for Band 13/5/8) and LTE middle/high band (M/HB, 1710–2690 MHz). Ant2 can cover the LTE M/HB in 1710–2690 MHz. In addition, very low envelope correlation coefficients (ECCs) less than 0.1 in the LTE M/HB for Ant1 and Ant2 can be obtained. That is, in addition to the coverage of the LTE LB, the dual‐feed U‐slot antenna can be applied for the 2 × 2 LTE M/HB MIMO operation. The antenna structure and operating principle of the dual‐feed U‐slot antenna are presented, and the antenna performance is verified by the experimental study.

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