yes you can simulate airmode, depends on your aircraft type of course as to how that can be done.
An ATC 601 or 600 for example will do the job for testing.
Depending on where you are and what system you op under, radio licence , B2 or equivalent needed to sign off.
Testing an ATC would normally require a setting a test squawk code.
Some sets have antenna cuffs that fit over the antennae others just use a small vertical antenna on a mount/ground plane.