||MIMO antennas in the metal-casing smartphone for 2 × 2 and 4 × 4 MIMO operation are presented.|
The first design includes four LTE antennas and two WLAN antennas and the second design includes four LTE antennas.
In the two designs, all antennas are disposed at the two short edges of the smartphone. In the first design, Antennas 1 and 3 can cover LTE 824~960/1710~2690 MHz.
Antenna 2 can cover LTE 1710~2690 MHz and GPS operation. Antenna 4 can cover LTE 1710~2690 MHz. Antennas 5 and 6 can cover WLAN 2400~2500/5000~6000 MHz.
However, when Antennas 1 and 2 are excited, a strong coupling between the two antennas occurred in the high band,
which causes a high envelope correlation coefficient (ECC) thereof. Therefore, in the second design,
new four LTE antennas (Antennas 1 and 2 at the top short edge and Antennas 3 and 4 at the bottom short edge) are devised to achieve low ECC and good isolation.
The main feature of the second design is that the radiating metal-frame of Antenna 2 is shorted-circuited to the system ground plane between the two feed ports of Antennas 1 and 2,
so that the shorted metal-frame can also be used to direct the excited surface currents in the system ground plane.
In this case, good isolation and low ECC between two LTE MIMO antennas can be obtained.
In this design, Antennas 1 and 3 can cover LTE 880~960/1710~2690 MHz. Antennas 2 and 4 can cover 1710~2690 MHz.
The four LTE MIMO antennas can be applied in the 2 × 2 LTE low-band MIMO and 4 × 4 LTE high-band MIMO systems.