Do you mean a patch antenna? If yes, then I would propose to use the lowest Er substrate you can find (Ultralam2000 from Rogers would be a good candidate). I've done a prototype patch antenna for 20GHz, fed by coax line.
i design my antenna with IE3D and i would like to feed it with a microstrip line but it isn't possible for me to math it because i found for Zin antenna a complexe Z. i want to match it to 50Ω. how can i do.
is the minimum on S(1,1) dB graph(resonant frequency) is the point who Z=R on a smith graph ?