Fields from both dipoles combine to create circular or elliptical polarization. Reflectors may improve upward radiation.
Antennas · F1SYH
Turnstile antenna
The Turnstile combines two perpendicular dipoles fed 90 degrees out of phase.
VHF
Satellites
Polarisation circulaire
Operating principle
Main characteristics
Typical gain
Faible à modéré
Impedance
Adaptation et phasage nécessaires
Polarization
Circulaire ou quasi circulaire
Difficulty
Avancée
Dimensions and design
Each dipole is near half a wavelength. The quarter-wave phasing line must include cable velocity factor.
Construction and tuning
Step 1
Build two identical dipoles.
Step 2
Mount them at right angles.
Step 3
Build a 90-degree phasing line.
Step 4
Check phase order.
Step 5
Add a reflector if required.
Step 6
Check SWR and polarization.
Advantages
- Good sky coverage.
- Satellite-friendly polarization.
- Rotor not always required.
- Suitable for VHF and UHF.
Limitations
- Critical phasing network.
- Moderate gain.
- Possible elevation nulls.
- Requires accurate construction.
History and origin
The Turnstile was used for broadcasting and early space communication because of its circular polarization.
Safety
Weatherproof and mechanically secure the crossing and phasing network.