Understanding Antenna Polarization

A radio wave is made up of both electric and magnetic fields. In free space, the electric and magnetic fields are mutually perpendicular and are also perpendicular to the direction of propagation. The direction of oscillation of the electric field component, when a radio wave is propagating in a medium, is called the polarization of the radio wave.

Antennas are usually developed to receive and transmit radio waves that are polarized in a specific way. The different types of polarizations are discussed below:

Linear Polarization

When the electric field is oscillating in the horizontal or vertical direction, the radio wave is said to be linearly polarized.

Slant Polarization

When the electric field oscillates at –45 degrees and +45 degrees from a reference plane of 0 degrees, the polarization is said to be slant. It is another form of linear polarization, it is equivalent to taking a linearly polarized radio wave and rotating it 45 degrees.

Circular Polarization

When the polarization of a radio wave rotates while the signal propagates. Based on the direction the signal is rotating, circular polarization can be classified as two types: Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP). A Circularly Polarized signal consists of two perpendicular electromagnetic plane waves of equal amplitude, which are 90 degree out of phase.

Elliptical Polarization

Elliptically polarized radio signals consist of two perpendicular waves of unequal amplitude which differ in phase by 90°.