What are FCC Signal Booster guidelines & where to find them?
The FCC regulates cellphone signal boosters as it does any other device or amplifier that uses frequencies for amplification purposes. The FCC specifies which antennas may be used, how much gain an amplifier may have and even that an amplifier needs to be registering with a provider. These laws help the FCC regulate communications so that cellular towers, providers and emergency responders can communicate effectively. If this was not regulated, it may be detrimental to communication for many users. The regulations were last revised in 2014 and may be revised again in future.
This link to Electronic Code of Federal Regulations will help you understand the FCC guidelines and restrictions: https://www.ecfr.gov/cgi-bin/text-idx?SID=2dfb8555423ebf29ff89b25afdb970db&mc=true&node=se47.2.20_121&rgn=div8