Anritsu MS2024A/MS2026A - Antenna Calculations

Chapter 4 — Spectrum Analyzer 4-17 Field Strength
MS20xxA VNA Master UG 10580-00166 Rev. C 4-17
Antenna Calculations
The following is a list of various antenna calculations should you find it necessary to convert
from one to another:
Conversion of Levels from W to V
Conversion of signal levels from W to V in a 50 ohm system:
where:
P = power in Watts
V = voltage level in Volts
R = resistance in ohms
Note that:
and
For power in dBm, and voltage in dB (µV):
.
Power Density
Power density to field strength. An alternate measure of field strength to electric field is
power density:
where:
E = field strength in V/m
P = Power density in W/m
Power Density at a Point
Power density at a point is equal to:
In the far field, where electric and magnetic fields are related by the impedance of free space,
where:
P
d
= power density in W/m
P
t
= power transmitted in Watts
G
r
= gain of transmitting antenna
r = distance from the antenna in meters
P
V
2
R
-------=
1mW 10
3
W =
1μV10
6–
V=
V
dB μV()
P
dBm()
107dB+=
P
d
E
2
120π
-------------=
P
d
P
t
G
t
×
4 π× r
2
×
------------------------=
10580-00166C.book Page 17 Thursday, February 21, 2008 12:52 PM