ETS-Lindgren 3161 Octave Horn Antenna - Manual (Page 29)

E QUATION 2
dB(mW /m 2 ) = dB( μV/m)-115.8
The constant in this equation is obtained by considering the
Poynting vector which relates the power density in (W/m
2
) to the
electric field strength in (V/m) by:
P =
E 2
η
Where η is the free space characteristic impedance equal to 120 π Ω.
Transforming the previous questions to decibels and using the
appropriate conversion factors to convert dB(W/m
2
) to dB(mW/m
2
) for
power density and dB(V/m) to dB(µV/m) for the electric field, the
constant becomes:
30 120 10 120 115 8
10
− − = − log ( ) . π
E QUATION 3
dB( μV/m) = dB(μV) + AF
E QUATION 4
V/m = 10
dB ( V/m)-120 μ
20
E QUATION 5
dB ( μA/m) = dB(μV/m) - 51.5
The magnetic field strength is related to the electric field strength via
the characteristic impedance of free space. When the transformation is
made to decibels, the constant becomes:
20 120 51 5
10
log ( ) . π =
Radiated Emissions Measurements | 29