Orbiting/loitering around flight path

Looking for a way to easily plan a flight where the plane will follow an overall path but continuously fly in a circular motion orbit. The path would ultimately be a spiral along a line, looking a little like a Spirograph image (if you’re old enough to remember those). The idea is to rotate a directional antenna 360º along a flight path with the gain side pointing toward the center. Radius of the orbit would probably be about 100-300 meters or so, TBD after a few test flights.