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Antenna Factors
Field Strength Units
Field Strength Units
Radiated EMI emissions measurements measure the electric field. The field strength
is calibrated in dBμV/m. Field strength in dBμV/m is derived from the following:
Pt = total power radiated from an isotropic radiator
PD = the power density at a distance r from the isotropic radiator (far field)
PD = Pt /4πr2
R = 120mΩ
PD = E2/R
E2/R = Pt /4πr2
E = (Pt x 30)1/2 /r (V/m)
Far field
1
is considered to be >λ/2π
Antenna factors
The definition of antenna factors is the ratio of the electric field in volts per meter
present at the plane of the antenna versus the voltage out of the antenna connector.
NOTEAntenna factors are not the same as antenna gain.
1. Far Field is the minimum distance from a radiator where the field becomes a planar wave.
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