hello,
please be more specific. omnidirectional antennas do not exist. "omnidirectionality" means radiation in all theta, phi directions, and all real antennas have some preferred directions (they are directive).
also, omnidirectional antennas do not have polarization information (radiation is the same regardless the polarization), and this does not either exist.
the unique omnidirectional source is a point source, which is a theoretical concept.
probably do you mean low gain antennas?
rgdz.