Turnstile Antenna
Understanding Turnstile Antennas
The turnstile is one of the simplest antennas for generating circular polarization. Two crossed dipoles with quadrature feeding produce CP in the broadside direction. The handedness (RHCP or LHCP) is determined by the direction of the 90-degree phase lead.
Turnstile Properties
- Pattern: Omnidirectional in the horizontal plane (like a dipole but with CP).
- Gain: About 2 dBi for a single turnstile. 5-8 dBi for stacked arrays.
- Axial ratio: Near-unity (good CP) on axis, degrades off-axis.
- Bandwidth: Similar to a dipole, about 5-10%.
Stacked Turnstile Arrays
Multiple turnstile elements stacked vertically with proper spacing and phasing produce a narrowed beam in the vertical plane, increasing gain while maintaining CP. Stacked turnstile arrays with reflectors are commonly used for satellite ground stations.
Frequently Asked Questions
What is a turnstile antenna?
A turnstile is two crossed dipoles fed with 90-degree phase difference to produce circular polarization. It provides omnidirectional CP coverage in the horizontal plane. Used for satellite communication, weather satellite reception, and broadcasting.
How does a turnstile produce circular polarization?
The two dipoles radiate orthogonal linear fields. The 90-degree phase difference between the feeds causes the resulting electric field vector to rotate, producing circular polarization along the broadside direction.
What is a turnstile antenna used for?
Satellite telemetry and command at VHF/UHF, NOAA weather satellite image reception (137 MHz), VHF FM broadcasting (horizontally polarized version), and amateur radio satellite communication.