If using multiple converging lasers, the antenna need not be connected to the equipment. Two lasers could ionize the air in a line 2500m long, and a third could excite the center of it in a modulated fashion. That would be transmit only, unless you had some way to measure the energy levels at that center point from a distance.
It would be unlikely to glow brightly enough in the visual spectrum to see in the daytime, but it would be pretty cool at night.
It would be unlikely to glow brightly enough in the visual spectrum to see in the daytime, but it would be pretty cool at night.