https://phys.org/news/2018-07-qualcomm-antenna-technologies-power-super.html

Some harness millimeter wave radio frequencies to deliver fiber-optic like speeds. That potentially solves a stubborn technical puzzle surrounding 5G: How to make antennas that are small enough for use in smartphones but also capable enough to receive finicky millimeter wave radio signals that are susceptible to interference.

Some industry experts have questioned whether it was technically feasible to miniaturize antenna technologies so smartphones could tap millimeter wave frequencies—or at least doubted it was possible by the time the first 5G wireless networks begin rolling out in 2019.