Anritsu Field Master MS2070A - Antenna Calculations

Spectrum Analyzer Measurements 3-5 Field Strength
Spectrum Analyzer MG PN: 10580-00447 Rev. H 3-17
Antenna Calculations
This section provides a list of various antenna calculations to convert from one unit of measure to another.
Definitions
P = power in watts
V = voltage level in volts
R = resistance in ohms
Note that 1 mW = 10
–3
W and 1 µV = 10
–6
V
E = field strength in V/m
H = magnetic field strength in A/m
Z
0
= characteristic impedance of vacuum, 120π ohm ~ 377 ohm
P
d
= Power density in W/m
2
r = distance from antenna in meters
AF = antenna factor, ratio of incident electromagnetic field to the output voltage
A
e
= antenna equivalent area
g = antenna gain as power ratio
G = antenna gain in dBi
C
0
= speed of light in vacuum, 299,792,458 m/s
Equations
P = V
2
/R
V
dBµV
= P
dBm
+ 107 dB
A
e
= g(λ
2
/4π)
G = 10*log(g)
g = 10
G/10
= (9.73/λ10
AF/20
)
2
ƒ = C
0
/λ
P
r
= A
e
P
d
P
d
= P
t
G
t
/(4πr
2
) (Power density at a point)
P
d
= E
2
/Z
0
= E
2
/120π = Z
0
H
2
E = Z
0
H = √(P
d
120π)
AF = 20*log(9.73/
λ√g)
The field strength equations are only valid in the far field, where electric and magnetic fields are related by the
characteristic impedance of free space.