Ericsson M3090, Руководство интегратора

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About Antennas 15
M3090 Integrator’s Manual, Doc.no: 198 17 - KRD 102 303 Uen, Rev B
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Antenna gain is defined as the ratio between the antenna’s radiant intensity and
that of a reference antenna which experiences no loss, but has the same power
input.
Antenna gain is usually expressed in dBi, the i indicating that the calculated
radiation from an isotropic antenna has been used as a reference. The isotropic
antenna has the same radiant intensity in all directions, that is, the radiation
pattern is spherical.
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In data sheets, an antenna’s maximum gain is often expressed in dBd
without any reference to direction. The (second) d in dBd indicates
that the calculated radiation from a single half-wave dipole antenna
is used as a reference.
The relationship between dBd and dBi is described in
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The antenna must have sufficiently effective radiation for the radio terminal to
be able to communicate with a radio base station. The maximum range might
be up to 15 or 20 kilometres depending on:
• what frequency range the Mobitex network uses (the higher the frequency,
the shorter the maximum distance);
• whether the terminal is situated in a built-up area or in open country.
In an urban area, attenuation caused by buildings, walls and other obstacles has
to be considered. Too large or too many obstacles around the antenna might
mean that the radio terminal cannot establish a contact with the radio base
station. In such a case, the antenna is said to be in a radio shadow.
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dBd = dBi + 2.15 dB
P(d) = P(i) x 1.64