Reference antenna

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A reference antenna (also reference antenna ), to which a comparison antenna that is used gain a directional antenna to capture relative to the reference antenna numerically. Reference antennas are considered to be free space radiators; H. the gain is related to a radiator in free space, without the influence of the earth's surface.

Antenna types used

The main reference antennas used are:

The half-wave dipole is usually used for comparison purposes, as it can best be realized in practice under reproducible conditions. However, it is also difficult to implement, since on the one hand it should be as thick as possible in order to guarantee low losses, and on the other hand it should be as thin as possible, since this is the only way to guarantee sinusoidal current distribution.

Which reference antenna was used as a comparison when determining the profit must also be specified, since the numerical value of the profit depends on this. A small letter is often added to the measured values , usually given in decibels  (dB) :

Conversion of profit values

Influence of the antenna type

The measurement results are usually converted to the spherical emitter, as it is easier to calculate (e.g. with the radiation power ):

  • for the Hertzian dipole, the radiation intensity in the main direction is higher than the reference value by a factor of G = 1.5 (1.76 dBi).
  • with the half-wave dipole this antenna gain G is a factor of 1.64 (corresponds to 2.15 dBi).

Example: an antenna with a gain as a power factor of 100 has a value of 20 dBi in relation to the isotropic radiator. Based on the Hertzian dipole the same antenna has a gain of 66, 66 (corresponding to 18.24 dBd).

The profit related to the shot peen is called absolute profit , any other profit indication is a relative profit .

Influence of polarization

The reference antennas (including the isotropic radiator) are assumed to be linearly polarized . For the measurement of circularly polarized antennas, own reference antennas, specially calibrated for this purpose, are used in practice , whose own antenna gain is added as an indication in decibels to the measured comparative value of an examined antenna - or (if indicated as a factor) multiplied by the measured comparative value .

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