Balluff BIS U Basishandbuch Seite 46

BIS U Basic Manual
6
Calculating the Radiated Power
16
The measurable value in the main dispersion direction always defines the radiated antenna
power. Within the jurisdiction of the EU, limit values relating to the power radiated from antennas
are calculated using what is known as Effective Radiated Power (ERP) based on a half-wave
dipole.
Therefore, the ERP value describes the effective power that a dipole antenna supplied with P
radiates in the preferred direction. The ERP value of an antenna whose gain is defined based on
an isotropic radiator is calculated according to the following equation:
ERP = P + G – 2.15 dBi with
0 i
Effective radiated power in relation to an isotropic radiator (Effective Isotropically Radiated Power
or EIRP) is another way of indicating radiated power. Radiated power in the form of EIRP values
are common in the USA, as well as in other countries.
The equations for calculating the radiated power of antennas are logarithmic and the power data
is standardized to 1 mW because addition is simpler to perform. As a result, all required antenna
and power parameters can be specified in decibels and simply added to one another.
The following parameters are required or used to calculate the radiated antenna power:
P [dBm]
0
G[dBic]
G[dBi] = 2.15 dB
half-wave dipole
Ak[dB]
L[m]
This can be used in the following formula to calculate the equivalent radiated power of an
antenna based on a half-wave dipole:
(1) ERP[dBm] = P [dBm] – Ak[dB] • L[m] + G[dBic] – 2.15 dB
0
EIRP[dBm] = P [dBm] – Ak[dB] • L[m] + G[dBic]
0
The formula can be rearranged to calculate the permitted socket power of the processor unit:
(2) P [dBm] = ERP[dBm] + Ak[dB] • L[m] - G[dBic] + 2.15 dB
0
P [dBm] = EIRP[dBm] + Ak[dB] • L[m] - G[dBic]
0
Watts
4.000
2.000
1.000
0.500
0.250
0.125
4.000
Table 1: Correlation table
P [dBm] Antenna supply power
0
G [dBi] Antenna gain based on isotropic radiator
i
2.15 dBi Gain of dipole based on isotropic radiator
Socket output power of the processor unit based on
1 mW
Circular antenna gain based on the
isotropic radiator
Antenna gain of half-wave dipole
Cable attenuation per meter
Cable length in meters
POWER
0
dBm
36
33
30
27
24
21
36