Antenna Gain - While the gain definition assumes ideal matching between the antenna and the connected cable and receiver or transmitter, in practice this is rarely the case. So what is measured in a non-ideally matched setup is called the practical gain of an antenna. The gain can be determined from the practical gain with the following formula:
where the amount of mismatch is expressed by the magnitude of the reflection coefficient r.
Corresponding to the directivity factor, the gain G is the ratio of the radiation intensity Fmax obtained in the main direction of radiation to the radiation intensity Fi0, that would be generated by a loss-free isotropic radiator with the same input power Pt0.
In contrast to the directivity factor, the antenna efficiency η is taken into account in the above equation since the following applies:
For an antenna with efficiency η = 100%, this means that gain and directivity are equal.
In practice this is hardly the case, so the gain, which can be easily determined during measurements, is the parameter which is more frequently used.
Gain and directivity are often expressed in logarithmic form:
In practice this is hardly the case, so the gain, which can be easily determined during measurements, is the parameter which is more frequently used.
Gain and directivity are often expressed in logarithmic form:
Contrary to common rules and standards, it is well established practice to indicate the reference with an additional letter after dB:
ı dBi refers to the isotropic radiator
ı dBd refers to the half-wave dipole
For example the following conversion applies: 0 dBd ≈ 2.15 dBi.