The Turnstile antenna is one more kind of array antenna. The shape of this array represents the turnstile, which is used at the appearances of few places. This antenna has a wide range of military applications.
The frequency range in which the turnstile antennas operate is around 30 MHz to 3GHz which belong to the VHF and UHF bands.
Two equal half-wave dipoles are located at right angles to each other and are fed inphase. These dipoles are excited 90° out of phase with each other. Turnstile array can also be termed as crossed dipoles array.
The beyond images explain turnstile antennas.
To offer high directivity, several turnstiles may be stacked along a vertical axis, and are phased as shown in the figure given beyond. The polarization of these turnstile antennas be contingent upon their mode of operation.
The pair of such dipoles frequently stacked, is known as BAY. In the figures revealed above, two bays are spaced half wavelength (λ/2) apart and the corresponding elements are fed in phase. The radiation yield by the combination of bays results in better directivity.
The resulting are the modes of operation of a Turnstile antenna.
In Normal mode of operation, the antenna radiates horizontally polarizedwaves which are perpendicular to its axis.
In Axial mode of operation, the antenna emits circularly polarized waves beside its axis i.e. parallel to its axis.
For circular polarization, the transmitter radiating with right-circular polarization must have a receiver with same right-circular polarization and vice versa. If it is left-circular polarized one, unlike the transmitter, there will be a severe loss of gain.
For a turnstile antenna, the radiation power is 3dB below the maximum radiation of a halfwave dipole radiating the same power. Hence, to overcome this drawback, the Super-turnstile antenna is built.
The modest dipole elements in turnstile are swapped by four flat sheets in Super-turnstile. The design of Super-turnstile array is such that 1 to 8 bays can be constructed on a single mast. The other name for Super-turnstile antenna is the Batwing Antenna.
The beyond images show super-turnstile antenna. Figure 1 displays the planning of superturnstile array with the red dots being the feed points. Figure 2 shows the stacked turnstile array used in satellite communications.
The radiation pattern will be parallel to the radiation pattern of two super imposed dipoles. Though it is close to omni-directional pattern, it leaves a cloveleaf shaped pattern.
The beyond figure shows the radiational pattern of a turnstile array. The characteristic figure-ofeight patterns were united to yield a closely circular pattern.
The resulting are the advantages of Turnstile antennas −
The resulting is the disadvantage of Turnstile antennas −
The resulting are the applications of Turnstile antennas −
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