Turnstile antenna
Encyclopedia
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
s aligned at right angles to each other and fed 90 degrees out-of-phase. The name reflects that the antenna looks like a turnstile
Turnstile
A turnstile, also called a baffle gate, is a form of gate which allows one person to pass at a time. It can also be made so as to enforce one-way traffic of people, and in addition, it can restrict passage only to people who insert a coin, a ticket, a pass, or similar...
when mounted horizontally. When mounted horizontally the antenna is nearly omnidirectional
Omnidirectional
Omnidirectional refers to the notion of existing in every direction. Omnidirectional devices include:* Omnidirectional antenna, an antenna that radiates equally in all directions* VHF omnidirectional range, a type of radio navigation system for aircraft...
on the horizontal plane. When mounted vertically the antenna is directional to a right angle to its plane and is circularly polarized. The turnstile antenna is often used for communication satellites because, being circularly polarized, the polarization of the signal doesn't rotate when the satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
rotates.
The principles of the turnstile antenna are also applicable to Yagi
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
and Log-periodic antenna
Log-periodic antenna
In telecommunication, a log-periodic antenna is a broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency...
s.