A.H. Systems SAS-571 Manuale operativo - Pagina 12
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A.H. Systems AK-571-4 Horn Antenna Kit
The constant in this equation is derived following similar logic. First, consider the Poynting Vector
which relates the power density (W/m
Where is the free space characteristic impedance equal to 120
decibels and using the appropriate conversion factor to convert dBW/m
density and dBV/m to dBV/m for the electric field, the constant becomes 115.8
Where AF is the antenna factor of the antenna being used, provided by the antenna manufacturer or
To derive the constant for the above equation, simply convert the characteristic impedance of free
The derivation for the constant in the above equation comes from the decibel equivalent of the factor
In this equation, the constant 2.0 is derived as follows. The magnetic flux density, B in Teslas (T), is
related to the magnetic field strength, H in A/m, by the permeability of the medium in Henry's per
Converting from T to pT and from A/m to A/m, and taking the Log, the constant becomes...
A.H. Systems inc. – Apr 2020
REV C
dBmW/m
) to the electric field strength (V/m) by the following equation.
2
dBV/m = dBV + AF
a calibration that was performed within the last year.
Not much to this one, just plug away!
dBA/m = dBV/m - 51.5
space to decibels, as shown below.
20Log
As above, simply plug away.
dBW/m
A simple relation to calculate decibel-Watts per square meter.
dBmW/m
of 1000 used to convert W to mW and vice versa, as shown below.
dBpT = dBA/m + 2.0
meter (H/m). For free space, the permeability is given as...
240 - 120 + 20Log
dBpT = dBuV + dBpT/uV + Cable Loss
dBuV/m = dBpT + 49.5 dB
= dBV/m - 115.8
2
P=|E|
/
2
V/m = 10
{[(dBuV/m)-120]/20}
[120] = 51.5
10
A/m = 10
{[(dBuA/m)-120]/20}
= 10Log
[V/m - A/m]
2
10
= dBW/m
+ 30
2
2
10Log
[1000] = 30
10
= 4 x 10
H/m
-7
o
[4 x 10
] = 2.0
-7
10
. Transforming this equation to
to dBmW/m
for power
2
2
12