Polarization of an antenna is determined by:

By convention, the polarization of a radio wave is defined by the orientation of its electric field (E-field) with respect to the Earth's surface. If the E-field is vertical (perpendicular to the ground), the polarization is vertical; if it is horizontal, the polarization is horizontal. The magnetic field (H-field) is always at right angles to the electric field, but it is not used to define the antenna's overall polarization. Other options, like the transmission line orientation or the internal angle between the fields, are irrelevant to defining polarization.