In many pictures I see most soldiers have a big antenna on them. What is it? And does every soldier get one?

What you’re probably seeing is a multi-band intrateam radio (MBITR). Depending on the model, radios transmit and receive secure voice and data signals. The name of the game in ground combat is “shoot, move, and communicate.”

It's a radio antenna. Makes good targets for snipers.

RTO Radio Telephone Operator. Since you mention documentary's I take it they are older pictures you are probably seeing a squad or Platoon RTO carrying the old PRC-10 radio. Not every one nor even every squad had one.

The person you see in pics and documentaries that have those antennas....they are the most important person to that element. The RTO.

Are we sure it is not the jamming equipment some units use to jam phone and radio signals to IED's. I know we got trained on them in 2014 but since we flew everywhere never saw one used. We were actually trained on the vehicle mounted one and the troop mounted one. The troop mounted one was good for about 50' radius so only needed enough to cover what ever size your team was.