Antenna polarization is the orientation of an antenna’s electric field. An electromagnetic wave can be polarized to restrict its electric field to one direction; this principle is also behind polarized sunglasses, which block all light wave components that are oriented in a certain direction. Horizontal polarization means an electric field only points horizontally, for example, and a radio antenna that is polarized in this way will only receive the horizontal component of an incoming radio wave. Linear polarization is the simplest example, though circularly polarized antennas are also used.
An electromagnetic wave has a specific orientation that includes its direction of propagation. This is merely the direction of travel, such as from the Sun and toward Earth. A wave’s electric field, on the other hand, typically points at a right angle from the direction of propagation. It can point in any direction, in fact, as long as it is orthogonal to the direction of travel. Polarization, however, further restricts the orientation of this electric field.
In polarized sunglasses, sunlight is vertically polarized. Incoming light can be oriented in a variety of directions at the time it strikes a pair of sunglasses, and statistically speaking, the incoming light is equally distributed in the plane orthogonal to the direction of travel. Light reflections that cause glare, however, are typically oriented horizontally. What polarized sunglasses do is only allow the vertical component of light waves past their lenses; any part of a light wave’s orientation that is in the horizontal direction — such as with glare — will not pass through.
Antenna polarization refers to the polarization of the electric fields radiated by the antenna. Antennas emit and receive in the same manner, so polarization needs to be the same for two to communicate. There will be no reception for antennas with opposite orientations, which means that two sets of antennas can be polarized in opposite directions, and they will not interfere with each other. Radio and television broadcasts take advantage of this.
The simplest version is linear polarization, which is either horizontal or vertical. An antenna that is oriented horizontally will always produce an electric field that points horizontally. TV broadcasts are horizontally polarized, which explains why TV antennas have horizontal bars. Signals that have electrical fields with vertical components can also be received if they include horizontal components as well.