Antenna axial propeller

The Antenne axial propeller owes its name with the fact that it radiates mainly in its axis of winding. It was described for the first time in 1947 by John Daniel Kraus, a American Radioamateur .

Description

The antenna propeller resembles a Solénoïde stretched whose end is masked by a metal screen.

It is composed of:

reference mark S : aerial element, a wound rigid discussion thread as a spring
reference mark R : reflectors formed of a full sheet or a lattice
reference mark B : central support of the propeller
reference mark E : spacers maintaining the propeller on the central support
reference mark C : coaxial cable whose braid is connected on the reflectors and the heart at the end of the propeller via a device transformer aerial matching.

The propeller is often protected by a tube isolating avoiding the deposit from white frost on the whorls.

Characteristics

To obtain an axial radiation, it is necessary that the circumference of a whorl of the spring is about the Wavelength of the emitted signal and that the step of the propeller is close to the quarter this wavelength.

The profit of the antenna is, up to a certain point, proportional to the number of whorls and the Pas of rolling up (in other words with the length of the reel).

The Band-width of the antenna is relatively broad, being inversely proportional to the length of the antenna.

The polarization is circular and the direction of rotation depends on the direction of rolling up of the propeller.

The directivity of the antenna is relatively low, the aperture of an antenna of 10 whorls is of approximately 30 degrees.

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