Polarization

Polarization describes the orientation of the radio wave’s electric field — and matching it between two antennas matters a great deal.

Linear: vertical and horizontal

A vertical antenna radiates a vertically polarized wave; a horizontal dipole, a horizontal one. Two stations communicate best when their antennas share polarization. A 90-degree mismatch (cross-polarization) can cost 20 dB or more — a severe loss.

Circular polarization

Some antennas, like the axial-mode helical, radiate a wave whose field rotates as it travels — circular polarization. This is invaluable for satellites: as a spacecraft tumbles, or as the ionosphere rotates the wave (Faraday rotation), a circularly polarized link keeps working where a linear one would fade.

Practical choices

• Vertical for mobile and omnidirectional ground coverage
• Horizontal for long-haul HF and to reduce man-made noise
• Circular for satellites and any link with rotating geometry

A crossed-dipole turnstile fed in quadrature is a common way to generate circular polarization for satellite work.