Polarization is a property of electromagnetic waves that can oscillate with more than one orientation. By convention, the orientation of the wave’s electric field at a point in space over one period of the oscillation specifies its orientation.

The magnitude and direction of an electric field is defined by what is called an electric field vector. The Galileo transmitted signals are Right-Hand Circularly Polarized (RHCP), which means that the electric field vectors have a constant magnitude but the direction changes in a rotary manner. If the wave is frozen in time, the electric field vector of the wave describes a helix along the direction of propagation.

The right handedness is determined by pointing one’s right thumb in the same direction that the wave is propagating, and matching the curling of one’s fingers to the direction of the temporal rotation of the field.

It will be understood better with an animation of a right-handed circularly polarized wave:

RHCP wave