The following link discusses wind turbine towers but the info is equally applicable to antenna towers. Lot's of links and good reading.
Lightning Protection
Lightning Protection
Any one ever read over Motorola R56 regarding communications sites? If you want to have the best grounding ever, read this:
https://sites.auburn.edu/admin/facilities/spw-bid-calendar/11-150 AU Regional Airport-Construct a Self-Supporting Radio Tower/Project Documents/1/Motorola_R56_2005_manual.pdf
All of the communications sites that I own or maintain all meet this standard.
Q