There is no radar for this one. The structure looks like this and can be found floating in the sky in the End.

Under the meteoroid blocks on the left (marked by glowstone for the purpose of this guide), you can find the Meteroite Crystal, which is used to summon Deoxys. Under the meteoroid blocks on the left (marked by froglight for the purpose of this guide), you can find Deoxys' Shrine. Use the Meteroite Crystal on the shrine. He will spawn behind the shrine. The form he spawns in is random.

Climb up a little bit to the final cluster of meteoroid blocks to get the Deoxys Meteroite, which allows you to infinitely cycle through deoxys forms