From MediaTek: "MediaTek TAS 2.0 Smart Antenna in action"
Transmitting Antenna Switching (TAS) 2.0 is a MediaTek patented technology that actively detects the best antenna to use in a smartphone. In this example the antennas are placed at opposite ends or either side for maximum effect. This ensures no signal is blocked regardless of how the phone is held: portrait or landscape, in hands, or up to the ear. The result is a more reliable and sustainable connection, as well as lower power consumption that boosts battery life.
Source: https://www.mediatek.com/blog/video-see-mediatek-tas-2-0-smart-antenna-in-action