You do have to be registered with the ARRL as many of us are for QRZ.com but you don't have to be a paid up member of ARRL.
When you have gone through the quite lengthy order process and got a zero cost invoice, the download link is emailed to you and this can be quite some time after. Mine was about 20 min.
It's a big download about 1gig but if you are into antennas, really worth it.
Best73,
Ace
G0ACE