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A turnstile antenna is a set of two dipole antennas aligned at right angles to each other and fed 90 degrees out of phase. The name reflects that the antenna looks like a turnstile when mounted horizontally.
The antenna can be used in two different modes. When used in the normal mode, mounted with its axis vertical, the antenna is omnidirectional, radiating horizontally-polarized radio waves in all directions perpendicular to (normal to) its axis. When used in axial mode mounted with its axis pointing toward the receiver, it radiates circularly-polarized radio waves parallel to its axis. The axial mode turnstile antenna is often used for satellite communication because, being circularly polarized, the polarization of the signal doesn't rotate when the satellite rotates.
Yagi and log-periodic versions of the axial mode turnstile antenna can also be built, consisting of two identical Yagi or log-periodic antennas mounted along the same axis, with pairs of identical elements mounted at right angles, fed 90 degrees out-of-phase. The additional elements increase the gain of the main lobe on the axis and reduce the radiation normal to the axis. A reflector consisting of a metal screen or radial rods is often used at the opposite end of the antenna to reflect unwanted radiation back in the desired direction. This design is often used for satellite ground station antennas.
- Turnstile Construction plans for satellite communication
- Construction plans
- Turnstile design for APT weather satellite reception
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