Aperture coupled circular antenna

Hi All:
I am doing a master degree about Aperture coupled antenna. Can any one help me in finding a paper about the input impedance of the aperture coupled circular antenna. i have many papers about rectangular but not circular.
with regards to all

"A small dielectric resonator antenna"
M.T.Lee, K.M.Luk, K.W.Leung, and M.K.Leung
IEEE transactions on Antenna And Propagation,
vol. 50, NO. 10, Oct. 2002
Page: 1485-1487


Best Regards,