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User manual
Antenna model: AT3000
Rev 6.0 – September 2014
Clampco Sistemi is a registered trademark of
Calzavara SpA
– via Corecian, 60 – 33031 – Basiliano (Italy) http://www.clampco-sistemi.com/
3. AT3000 antenna characteristics
3.1. Radiation diagrams and Isotropy
AT3000 contains three short dipole antennas with linear polarization. The structure of these antennas makes
possible to obtain a transduction coefficient that is sufficiently high at low frequencies while maintaining an omni-
directional type radiation diagram even at the highest frequencies in the operating band. To achieve these
behavior the interaction between the 3 antennas and the effect of the antenna rod and of the cables have been
minimized.
It is well known that the invariability of the total field
in relation to the device orientation
selected for making the measurement (isotropy) is totally reliant on the availability of an omnidirectional diagram
for each of the three internal antennas.
From experimental diagrams obtained, it has been found that this characteristic is achieved with negligible
deviations from the lowest frequencies and up to about 1.7 GHz. Deviations from the omnidirectional diagram are
slight between 1.7 and 2.2 GHz and are still very small between 2.2 and 2.5 GHz.
It should be noted that the stochastic measurement error due to deviation from the omnidirectional
characteristics (anisotropy) is calculated on the quadratic sum of the three components. This means that over and
under-estimates of the individual component are normally compensated by reducing the error on the total field.
It should in fact be borne in mind that factor K is normally defined in a calibration with a wave striking the antenna
in a single given direction.
3.2. Antenna factor
To keep things simple, let us assume that the antenna is struck by a monochromatic, plane and uniform wave
whose polarization coincides with the axis of the dipole. The system consisting of the antenna and ferrite bead
coaxial cable returns a signal whose amplitude is proportional to the amplitude of the electric field being
measured. The proportionality factor depends on the geometric-electrical characteristics of the dipole, of the
internal balun and of the cable. The frequency of the incident wave remains the only parameter free of this
transfer, being negligible the variations of the transfer characteristics due to temperature variations, drift of the
construction component characteristics and variations in the condition of the connectors and cables. We can
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