No abstract

Two coupled‐fed loop antennas with a conjoined capacitor‐embedded section to achieve compact size and high isolation for the fifth‐generation (5G) multi‐input multi‐output (MIMO) operation in the tablet device are presented. The two conjoined loop MIMO antennas cover the 5G band of 3300‐4200 MHz, which is considered to be the largest contiguous frequency range potentially available for 5G mobile broadband services below 6000 MHz. The conjoined capacitor‐embedded section not only functions as a part of the resonant path of the two loop antennas but also behaves like a band‐pass resonant structure in the operating band. The latter makes the capacitor‐embedded section to have much lower impedance in the operating band, as compared to that of a simple strip section. This makes it capable of effectively attracting the surface currents on the ground plane excited by one loop antenna to be away from the feed port of the other loop antenna. The two loop antennas can hence exhibit high isolation, even though the two antennas are conjoined to have a simple integrated planar structure of compact size. The envelope correlation coefficient (ECC) of the two conjoined loop antennas is also very small, less than 0.1 in the operating band.

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.