2. Cell Telephony Base Station Antennas Radiation
Base Station Antennas are usually located in the middle of hexagon areas named as cells, which divide a large area having a cell telephony network, as it is shown in the following picture on the right. The density of these cells and the number of antennas is increased with the number of users per area. The Base Station Antennas located at the center of these cells look like the ones in the picture on the left.
Any cell telephony company has its own different cells network with antennas, something which increases the total electromagnetic pollution per area.
Electromagnetic Pollution by one only Base Station Antenna
There is strong interest about the level of pollution and its relation with the safety limit distance of nearest buildings from the position of one only radiating antenna.
The radiation patterns of common used antennas are anisotropic and their lobes cannot be calculated approximately by using the simple model of isotropic omnidirectional antenna.
In the picture on the left, you can observe the simulation of distribution of electromagnetic radiation of a typical base station antenna located on the wall of a tall building.
The position and kind of materials of each building around it, can give impressive results because of propagation phenomena (i.e. multi-reflections), like stronger fields (red color) even in areas far away from the antenna against closer to it (green color). This fact, and other kind of phenomena not mentioned here, make useless any proposal of a safety distance limit i.e. 300 metes, between an antenna and a building.
Electromagnetic Pollution by many Base Station Antennas
The existence of many antennas in one area makes more difficult the calculation of a standard safety distance limit from an antenna. This limit depends on each antenna (i.e. frequency, power, position, kind of antenna), the surrounding buildings construction, the weather and other factors.
In the picture on the left, you can observe one more simulation of electromagnetic radiation emitted by many antennas distributed to an urban area. The positions of maxima of this radiation are presented with red color and of minima with blue colors.
As you can see, the distribution of radiation is not the same at each area and height. So, a simple monitoring of electromagnetic fields with sensors of the emitted radiation by a cell telephony network, near or far from each antenna, is not a secure way to patrol an urban area.
Extra Covers of Cell Telephony Base Station Antennas
Extra covers of any kind to base station antennas are not permitted, neither for “extra” protection nor to “fit better” to the environment, as they can change their technical characteristics.
Good quality antennas sold by companies have their own protection materials named “radome” which have been passed specific tests i.e. weather changes, absorption behavior etc. in special labs.
In picture on the left, white and gray colored radome materials are used to cover the inside wired structure of different kind of antennas.
2.3.1. One example, which must be avoided
Greece is a less-developed country and this fact is verified every day in many aspects. Here is one…
Greek Atomic Energy Commission (GAEC) is a state authority responsible for protection of the population from electromagnetic pollution (ionic and nuclear). According to this authority base station antennas are permitted to be covered with extra covers in order to “fit better” to the environment. In the following, I show you a representative case.
In the first picture on the left, two base station antennas are installed – on the top of a building – inside two chimneys somewhere in Athens.
In the lower picture on the left, you can observe inside these chimneys big metallic elements (green circles) in front of the antennas, which make them parasitic ones.
It seems, that the members of GAEC know neither “what parasitic antenna” is nor “what radome” is.
It should be mentioned that the addition of such kind of extra materials around antennas (metalic elements or extra covers) by the cell telephony companies goes against the law. The effect of them to the radiation patterns of antennas is not included to their application study to GAEC, which checks it and gives them the permission to proceed.
The above case is a “common situation” in Greece and many antennas systems of unspecified construction have been installed on many buildings. The weight of these systems can be of great danger in case of a big earthquake.
I hope soon European Union will help Greece to undrestand the problems of this situation, by giving appropriate common instructions to all its member states.
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