What is Polarization of an Antenna?

What is Polarization of an Antenna?

Polarization of an antenna is the direction of electric field produced by the antenna. This would determine the direction of transmission and reception of the antenna. Usual antennas have linear polarization which could be vertical or horizontal depending on the plane in which electrical field of the antenna oscillates. There is also circular polarization in which the radio wave rotates as the signal propagates. If it rotates to the right, it is known as right hand circular polarization (RHCP) and if it rotates to the left, as left hand circular polarization (LHCP). I have come across these terms being used by radio amateurs who work through Ham Radio satellites.

Signals from a horizonal dipole will be horizontally polarized while that from a vertical dipole will be vertically polarized. For propagation by line of sight or ground wave, the polarization will not change during propagation. So receiving a vertically polarized signal using a horizontally polarized antenna would give poor results. But reflection from the ionosphere in case of sky wave can change the polarization.