Since the subject came up:
Main Deflector Dish
The main deflector is designed to handle all of the ship's high output long-range deflector beams. It works on a similar principle as warp fields, except in this case the deflector beam is a kind of subspace megaphone, generating a wave form in the very fabric of space-time itself. What makes it a deflector/tractor beam, of course, is that the wave form has a specific sawtooth pattern angled away/towards the source so that any object caught in the beam experiences acceleration in one direction or another. With advanced enough technology you could use this principle as a weapon
(which the Borg do with their tractor beams to literally shake their enemies apart) but this is normally not practical.
The main deflector has three main functions. Firstly, under impulse power it serves either to push obstructions out of the ship's path, or--primarily--as part of the bussard collectors
, which are mounted on the engineering hull behind and around the deflector. This placement is optimal since 1) the collector beam can sweep a wide area in front of the ship to draw alot of material during refueling operations and 2) it simplifies the storage and hydrogen pulled in by the ramscoop, which goes straight from the collector into storage tanks in the engineering hull where it can either be reacted with antimatter or converted TO antimatter for consumption later. The second function of the main deflector is for long range communications. Subspace radio involves the use of a standard radio signal piggybacked on a moving gravitomagnetic wave which can travel at nearly any speed, depending on how much power you can put into your deflector pulse; the more powerful your deflector, the faster your message reaches its destination. The Enterprise' subspace transceiver can send subspace signals over a short distance and can receive them over just about any distance, but sending a reply over interstellar distances would require the power of the main deflector dish. The third function of the deflector is, of course, to reinforce the ship's deflector screens.