aridas sofia said:
You raise an interesting point, because in the TM he calls the larger forward-facing dish the main sensor, and the smaller flanking dishes the deflectors. I got the impression the rings weren't there because the extensive housing that is around them on the heavy cruiser is not apparent, and the deflector function is being handled by those smaller dishes (which clearly weren't on the aft of the hull).
Perhaps those were added to the primary deflector behind the dish due to the size of the Federation
-classes hull silhouette? And then technology advanced beyond the need, perhaps? I dunno, just reachin', but enjoyin' the Trek Tech angle it's taken.
Regardless, I always thought that the need for the "sensor dish" was a bit too "retro", even in the early 1970's watching Trek in syndication. In fact, my first 18" 1701 model got the dish knocked off of it and I left it off, thinking it looked better with out it being there.