Amy. Interesting one! A "mast" means a radio mast or a radio tower according to the interpretation of Part 24 but there is no definition anywhere that I can find of "supporting structure". I think you just have to therfore take a commensense approach. A 'supporting structure' would be someting relatively small and ancilliary to the antenna like brackets, beams or poles where as a mast (or tower) would be something much bigger and capable of potentially accommodating more than one antenna, each of which might then have its own supporting structure! In your particular case how high is the pole? If it is say just big enough to raise the antenna above a parapet wall, then I would say it was a 'supporting structure' and not a 'mast'. Just my gut reaction as an 'ex' Enforcement Officer so I'll be interested to see what others have to say on the subject.
