I’m thinking high powered microwaves or even UHF from a banana antenna bobbing up and down, turning left and right. Like the landing radars around military bases. Somewhere around 100kW or so.
The radar operators used to knock the pigeons off of hangers that way. Just sweep the sky. Don’t want any actual aircraft around though.
I think law enforcement uses a microwave emiitter to “knock down” drones. Military drones may have enough autonomous control that severing a data link may not cause them to crash or automatically switch to a landing sequence.