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Safe Distance in Front of VEGA Antenna
The VEGA Very High Gain Antenna family has much higher gain than any other antenna on the cellular infrastructure market. Cellular Network operators, when installing the VEGA antenna on a roof-top or tower need to ask themselves if this kind of focused transmitted energy in front of the VEGA antenna is safe to humans working in its vicinity and what is the safe distance from the antenna when in front of the main beam.
In this respect it is important to bring a simplified calculation based on the international safety standards base of both the International Commission of Non-ionizing Radiation Protection (ICNIRP) as well as the FCC standards (47 CFR section 1.1307(b)). Both these standard requirements agree on the maximal safe RF radiation power per unit area (power density) of the human body which will be used herein.
This Technical note presents the estimated safe distance at the most extreme case based on the international RF radiation exposure limits standards.
2. Safe Distance in front of VEGA Antenna
The VEGA line antennas are unique in their high gain. This high gain is a result of the VEGA’s very narrow focused beam. Our analysis will calculate the safe distance at the most extreme conditions specifically when using the different cellular frequency bands and VEGA highest gain model for the specified frequency.
2.1 Safe exposure limit
The safe exposure limit is a function of frequency. At the lower frequency bands, the exposure limit is high as the human tissues are less sensitive. Above 1500MHz the exposure power density limit has been set by regulatory bodies to 10W/m2. At lower frequencies of 900MHz band the exposure power density limit has been set to 4.5W/m2 (fMHz/200).
2.2 VEGA antenna gain and EIRP (Effective Isotropic Radiation Power)
For the same reason we will consider the safe distance for the highest gain VEGA antenna operating at the higher band of 1710-2690 MHz . This is the VEGA model CP12WB or CP12HP with gain of up to +29dBi. CMP12HP and CMP12WB have gain of +23dBi.
EIRP is calculated by multiplying the electrical input power by the gain of the antenna.
Let us assume that the input power to the VEGA antenna is 20W (+43dBm) multiplied by the gain of the VEGA (+29dBi) will result in EIRP of:
EIRP[CP12]= 43dBm+29dBi= +72dBm which is translated to 15848 W
EIRP[CMP12]= 43dBm+23dBi= +66dBm which is translated to 4000W
The same way for VEGA CC12HP or CC12WB with gain of +23dBi the EIRP will be:
EIRP[CC12]= 43dBm+23dBi=+66dBm which is equal to 3981W
2.3 Calculating the safe distance from the VEGA front
To calculate the safe distance from the VEGA we will use the US FCC and European ICNIRP exposure limit of 10W/m2 or 1mW/cm2 at 2100MHz and 4.5W/m2 at 900MHz .
The safe limit distance is calculated by :
D[m]= SQRT(EIRP[w]/(4π x S))
Where S is the exposure limit in W/m2
By inserting EIRP= 15848W and S=10w/m2 for the CP12 antennas we will get the safe distance to be :
D[m](CP12)=SQRT(15848/(4π x 10)) = 11m
For the CMP12 antennas the safe distance will be:
D[m](CMP12)=SQRT(4000/(4π x 10)) = 5.6m
For the CC12 antennas the EIRP will be 3981W and S is 4.5W/m2 so the safe distance in front of the antenna will be
D[m](CC12)=SQRT(3981/(4π x 4.5)) = 8.4m
This short note is intended to bring the RAN engineers a short and simple estimation of the safe distance from the antenna when working in front of the VEGA while it is operational with 20W input power. Comarcom will carry no responsibility for any claims concerning this technical note.
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