I would imagine the antenna just strengthens the incoming signal. You could still get reception/communication if the gateway/router/modem was near enough and not a lot of electrical shit attached (I would imagine that would generate more noise that could interfere)?

As an example - if you have a motherboard on your computer that supports wifi and comes with a port/plug for an antenna, you could remove that antenna and still receive a signal (IDK about sending) but it would suffer more signal loss due to the lack of antenna.

All that is just a guess of course. People more knowledgeable than me could explain/clarify.