Antenna polarization

Polarization of an antenna is the polarization of the wave it radiates in a given direction (usually the direction of maximum gain): the figure traced by the tip of the electric field vector with time at a fixed point in the far field.

Types:

• Linear: E moves along a straight line. Occurs when there is one component, or two components in phase (or 180° apart). Vertical (e.g. vertical monopole) or horizontal (e.g. horizontal dipole).
• Circular: E rotates with constant magnitude. Needs two orthogonal components of equal amplitude and 90° phase difference. Right-hand (RHCP) or left-hand (LHCP), e.g. axial-mode helix.
• Elliptical: general case; two orthogonal components with unequal amplitude and/or a phase difference other than 0° or 180°.

  Linear     Circular     Elliptical
    |          .-.          .--.
    |         (   )        (    )
    |          '-'          '--'

Axial ratio AR = major axis / minor axis: 1 for circular, ∞ for linear.

Polarization loss factor: PLF = cos²ψ, where ψ is the angle between the wave and antenna polarizations. A vertical antenna receiving a horizontal wave gets PLF = 0 (no signal).