How to repair cellular antenne of Lumia 820?

Hi,

since a few days my Nokia Lumia 820 cannot connect to the cellular network any more. WiFi however works fine; the SIM card works with other phones, too.

When the problem started, the outage was just temporary and I could connect to the cellular network the other day. Now it’s completely gone…

I guess that the cellular antenna is not working. But I can’t find any information on it. So my questions are

• How can I doublecheck, if the cellular antenna is (not) working? (and thus is the cause of my problems)
• Where is the antenna located? Can it be replaced?
• Any other guess, what be the problem’s cause can be?

(Btw: ifixit seems to know only Lumia 822 devices - are these different phones or is it just a typo?)