It's an electro-magnetic pulse (EMP) which covers the RF spectrum. Drones control systems are designed so that when they lose communications with the controller for any reason, they land safely via their own on-board control system.
There is a YouTube video on about a young guy that made a gun out of a microwave oven magnetron. He showed how he can shoot down drones with it. A cool project that actually worked. Google, “homemade microwave ray gun”
The mfg calls it an "EMP". Obviously, it's not the same as a nuclear EMP. It would be much more limited in power and frequency spectrum. I would assume that it has to be enough power to take out the front end of the command receiver or the drone would simply recover once the EMP was over.