GNU/Linux Ubuntu 18.04 Alfa AWUS1900 Driver Setup Guide
Hi! The linked Tutorial Shows You Step-by-Step How to Install Alfa Network AWUS1900 Wireless 802.11ac Driver in Ubuntu 18.04 Bionic LTS GNU/Linux.
And the Ubuntu Bionic Alfa AWUS1900 Setup is based on the Realtek rtl8814AU Chipset Driver Installation.
Eventually, follow the included instructions to Download and Install RTL8814au Linux Firmware.