Agreed that they are dispersion-field limited but their inherent broadband and "directionality" can, if located far enough from the signal sources and destinations, solve some interesting comms situations. For example, metropolitan "relays" able to leap tall buildings in a single bound:). They can complement broader NVIS HF which is less reliable and narrow band.
On 12/31/18, Steven Schear <schear.steve@gmail.com> wrote:
> Retrorefltors are very useful. They are hard to beat for covert comms.
> Unfortunately, optical ones are limited by weather. Much more versatile,
> if possibly less covert, are radio types. Ultra lights the size of the Echo
> are now easily deployed via inflatable and UV regidification.
Retros point back, perhaps not so much useful for direct
comms outside their relative dispersion return fields.
Planar mirrors, lenses, over horizon, ionosphere, relays,
lofted nuke comms, etc are different.
https://en.wikipedia.org/wiki/Retroreflector
https://en.wikipedia.org/wiki/List_of_passive_satellites