In "The Force Awakens", the Millenium Falcon has a square satellite dish. This is because its original circular satellite dish was broken off while flying into the main reactor of the Death Star in "Return of the Jedi"

Here you can see the Millenium Falcon with its circular satellite dish

As they fly into the main reactor, the satellite dish gets broken off after hitting the interior of the Death Star

Here you can see the Millenium Falcon stationed on Jakku with a replacement square satellite dish