Turnstile antenna

In normal mode the antenna radiates horizontally polarized radio waves perpendicular to its axis.

[3] The radiation in these horizontal directions is often increased by vertically stacking multiple turnstile antennas (called "bays") fed in phase.

These stacked normal mode turnstile antennas are used at VHF and UHF frequencies for FM and television broadcasting.

The flat reflector reverses the polarization sense so the reflected waves are right-circularly-polarized.

By locating the reflector λ/4 behind the elements the direct and reflected waves are in phase and add.

Another common way to increase the axial mode radiation is to replace each dipole with a Yagi array.

[citation needed] This is because with circularly polarized waves the relative orientation of the antenna elements does not affect the gain.

[3][6] This method of changing the physical dimensions of the antenna element to yield quadrature currents is known as turnstile feeding.

A common shape today is the batwing or superturnstile antenna, used for television broadcasting in the VHF or UHF bands[8] The batwing shape of each element produces an antenna with wide impedance bandwidth.

The US Nike missile program made use of the axial mode for telemetry and used the modified dipole technique to force the quadrature currents.