I'm not sure if anyone knows how to answer this question but google and the stinking class book isn't helping. I need to find the formula to calculate the horizontal beamwidth in degrees of a ground-based air-surveillance radar system that operates at 1300 MHz with a maximum range of 200 nmi.

I've been staring this problem for about 1hr and 15 minutes. I think I'll just skip it and log onto onionbooty.com!!!