Thanks NSEU
In the video he displayed a table of Antenna Size vs Beam Width depending on it being X Band or C Band (it is an old video).
I understand the 737 to have an X Band radar (that's all the information I've been able to find published - Bill Bulfer's 737 Cockpit Companion)
So in his table an 18" antenna has a beam width of 5 degrees and a 24" antenna = 4 degrees.
Not quite the same figures as you've given but as you say his table may be based on the older style parabolic dish. Could you provide me with a source for the 737NG numbers as that's the type I'm most interested in.
Best regards