The direction of the electric field vector of an electromagnetic wave. All electromagnetic waves have electric and magnetic fields that are perpendicular to the direction of propagation. The electric field and the magnetic fields are orthogonal, i.e., perpendicular to each other. The simplest graphical representation is of one field along the x-axis and one along the y-axis, with the direction of propagation plotted along the z-axis, as illustrated in Figure P-6. The electric and magnetic fields are at the same frequency, although their amplitude may not be the same and they may be out of phase. Polarization can be planar (linear), circular, or elliptical. If the emitter, i.e., transmitter, causes the wave to take place in one plane, the wave is said to be a plane-polarized wave. If the amplitude of the electric and magnetic fields is constant and the fields are in phase, the polarization is said to be linear and is graphically traced in a straight line. If the two component fields are of the same amplitude and exactly 90 degrees out of phase, polarization is said to be circular, rotating in either a clockwise or counterclockwise direction, depending on which field is ahead of the other. All other conditions create what is known as elliptical polarization.The design of an electromagnetic transmitter determines the polarization of the emitted signal, the propagation characteristics of the signal, and the design of the receiver.The signal from a transmitter begins as planar, or linear, although reflections and other interactions with physical matter can change the polarization.Vertical polarization is used in AM and FM radio, and horizontal polarization in television. Satellites and terrestrial microwave systems use alternating horizontal and vertical polarization in adjacent frequency bands, which results in orthogonal signals that minimize the potential for mutual interference.Automobile headlights are horizontally polarized to provide a better view of the road. Sunglasses are vertically polarized to block glare (i.e., reflection) from water and snow, which reflect sunlight on a horizontal plane. See also amplitude, frequency, phase, propagation, and sine wave.