Antenna Calculations

The following is a list of various antenna calculations should you find it necessary to convert from one parameter to another:

Conversion of signal levels from watts to volts in a 50 ohm system:

P = V2/R

where:

P = power in Watts
V = voltage level in Volts
R = resistance in ohms

Note that 1mW = 10–3 W and 1µV = 10–6 V.

For power in dBm, and voltage in dB (µV):

VdB(µV) = P(dBm) + 107 dB

Power density to field strength:

An alternate measure of field strength is power density:

Pd = E2 / 120π

where:

E = field strength in V/m
Pd = Power density in W/m2

Power density at a point:

Pd = PtGt / (4πr2)

This equation is only valid in the far field, where electric and magnetic fields are related by the characteristic impedance of free space:

where:

Pd = power density in W/m
Pt = power transmitted in Watts
Gr = gain of transmitting antenna
r = distance from the antenna in meters

 

 

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