My DM has given me a Legendary Shield... What does it do?

[OldTrees1]

Create a new aura like the Paladin Auras. Make this aura a 20ft radius aura. Now the Paladin has a new defensive feature that cares about the positioning (and thus strategy) of the group.

The 5E Holy Avenger has this ability:
While you hold the drawn sword, it creates an aura in a 10-foot radius around you. You and all creatures friendly to you in the aura have advantage on Saving Throws against Spells and other magical Effects. If you have 17 or more levels in the Paladin class, the radius of the aura increases to 30 feet.

So like that, but a static 20ft and a different ability.