I have used CST to simulate DRAs.
CST copes quite well with these structures.
(although on the first instance i was a bit reluctant).
I studied DRAs operating in 1.8, 2.4, and 5GHz,
having narrow band, broadband and multiband responses.
Make sure that you define dielectric material properties
(er, tand) accurately and fully. You'll be surprised how sensitive a DRA
response is with these parameters!!
If not know about this yet, check book from Luk 'Dielectric
Resonator Antennas'.
Happy simuls!