ETS-Lindgren 3160 Pyramidal Standard Gain Antenna User Manual
Page 45
www.ets-lindgren.com
Radiated Emissions Measurements
45
E
QUATION
2
dB(mW /m
2
) = dB(
V/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:
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 (
)
.
E
QUATION
3
dB(
V/m) = dB(
V) + AF
E
QUATION
4
V/m = 10
dB ( V/m)-120
20
E
QUATION
5
dB (
A/m) = dB(
V/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:
P =
E
2