Which of the following establishes grounding requirements for an amateur radio tower or antenna?
Why Tower and antenna grounding is a building and electrical safety matter, so it is governed by the electrical code adopted where you live, typically based on the National Electrical Code (Article 810 covers radio and TV antenna systems, Article 250 covers grounding). Your local jurisdiction may amend or add to that, so the local code is the authority you must satisfy. FCC Part 97 says nothing about how to ground a tower; it leaves construction and safety details to local authorities.
Watch out Part 97 is tempting because it is the amateur rule book, but it covers licensing and operating, not electrical installation practice. FAA rules apply only to marking and lighting of tall structures near airports, and UL publishes product listings and recommendations that are not themselves law.
Grounding is a building issue, not a radio issue: check the local electrical code (NEC 810), not Part 97.