Answer to Question #11955 Submitted to "Ask the Experts"

Category: Micro/Radio Waves, Radar & Powerlines — Satellite Dishes

The following question was answered by an expert in the appropriate field:

Q

My daughter is planning to study in the United Kingdom (UK) at a university that is quite close to a satellite earth station which is now operating at full speed. Will my daughter have any health risks due to radiofrequency (RF) radiation emitted from the station?

A

The simple answer is no—there are no known health risks associated with exposure to RF energy emitted from satellite earth station antennas in normally accessible locations. This conclusion is based on a comparison of the science-based safety limits (published in contemporary international RF safety standards and guidelines) and the levels of RF energy found in and around satellite communication (SATCOM) earth station facilities similar to the facility near your daughter's UK university.

With respect to international RF safety limits, sound judgments can be made as to the safety of a physical agent based on the overall results of the pertinent scientific evidence (referred to by scientists as the weight of evidence). The reliable scientific evidence clearly demonstrates that biological effects associated with exposure to RF energy are "threshold effects." This means that effects are only associated with exposures above a specific intensity—regardless of the exposure duration.1 The threshold exposure levels above which potentially harmful effects might occur have been independently established and confirmed many times over during the past five or six decades and serve as the basis for contemporary RF safety standards and guidelines. The collective credible evidence, including the results of epidemiological studies of individuals exposed to radio waves and laboratory studies of animals exposed both short-term and throughout their entire lifetimes, has not demonstrated that exposure to RF energy at levels that comply with contemporary science-based safety guidelines, such as those of the American National Standards Institute/Institute of Electrical and Electronics Engineers (ANSI/IEEE) standards (IEEE 2005) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines (ICNIRP 1998), can affect biological systems in a manner that might lead to, or augment, any health effect.

In spite of speculations about the possibility of effects occurring at levels below the safety guidelines, the fact is that the only effects reliably demonstrated in humans or laboratory animals are related to RF exposure at levels far in excess of the guidelines. This is not to say that exposure to radio waves at any intensity cannot cause untoward effects. Exposures at levels far higher than the safety guidelines can lead to whole or partial-body heating and possibly burns from touching an object on which high RF currents are flowing.2 Compliance with the safety guidelines protect humans from these effects. The overwhelming consensus of the international scientific community is that as long as the system complies with science-based safety guidelines, there is no adverse health risk; i.e., exposure to RF energy at levels at or below the safety guidelines is safe. (For example, see "Statements from Governments and Expert Panels Concerning Health Effects and Safe Exposure Levels of Radiofrequency Energy [2010–2017]" at http://www.ices-emfsafety.org/expert-reviews/.)

A lot is known about the safety of electromagnetic energy at RF energies. What is important is that in spite of the tremendous amount of research that has been reported in this field over the past five or six decades, there is a complete lack of any reliable evidence showing that exposure to RF energy at levels below contemporary safety guidelines is harmful to humans, including children.

With respect to the SATCOM antennas, for some people, the size of a SATCOM dish affects their perception of hazard; i.e., the large size is perceived as being associated with an increased potential hazard. One reason for the large size is to achieve a high antenna "gain," which is necessary to produce the required narrow, well-collimated beam.3 Also, the large size is necessary to collect enough of the weak signals from the satellite to produce a usable signal. When compared with more familiar communication transmission systems, large-diameter SATCOM antennas with high gain require far lower transmitter power to produce a signal of specified intensity at a given distance; i.e., the larger the diameter of the antenna, the lower the required transmitter power and, consequently, the lower the power density directly in front of the antenna and at corresponding points off-axis. (Power density, i.e., power per unit area, is the quantity in which exposure limits are expressed.) Thus, contrary to the perception of some, large dishes actually are associated with lower potential exposure, not higher.

As indicated above, when considering the potential impact of a SATCOM transmitting antenna, it is important to understand that the energy from such antennas is transmitted in a very narrow, well-collimated beam, similar to that of a searchlight. (The beam divergence of a typical SATCOM uplink antenna is typically less than 0.25 degrees). The reason for this is to mitigate the potential for interfering with adjacent satellites (which may be only a few degrees away from the satellite of interest) and interference with (or from) point-to-point microwave radio (radio relay) systems, many of which operate at the same frequencies as the SATCOM uplinks. Moreover, in order for a SATCOM system to function properly, a clear unobstructed line-of-sight path is required between the earth station and the satellite. Thus, the antennas are situated such that buildings, structures, vehicles and, hence, people cannot be located in the beam path.4 Consequently, exposure of the public to RF energy from a SATCOM facility is far below the limits found in contemporary safety standards and guidelines.

Over the years typical exposure levels in the vicinity of SATCOM antennas have been carefully measured by many groups and found to be below the ambient RF background associated with more familiar services such as commercial broadcast (commercial radio, TV, etc.), i.e., many, many orders of magnitude below any RF safety limits, even at locations adjacent to the facility. This was clearly demonstrated in Vernon, New Jersey, in 1985 when the U.S. Environmental Protection Agency (EPA) made detailed measurements at twenty-five locations in and around an RCA Americom SATCOM facility (EPA 1986). This would certainly be the case at your daughter’s university in the United Kingdom.

In conclusion, based on a comparison of contemporary RF safety limits with the levels of RF energy emitted from SATCOM antennas in normally accessible locations, there are no known health risks associated with the RF energy emitted from the satellite earth station antennas in normally accessible locations on or off the UK university's SATCOM earth station property.

Ron Petersen

1 This is a completely different phenomenon than that associated with exposure to much more energetic forms of radiation called "ionizing radiation" (such as x rays, nuclear radiation, etc.), where exposures even at low levels might damage genetic material.

2 There are no components associated with the base-station installation where this is possible—not even the antennas themselves.

3 Gain is a measure of how well RF energy is focused into a narrow beam. To illustrate this concept, compare the brightness of an ordinary 100 watt (W) light bulb with that from a 100 W spotlight (i.e., a focused beam). Even though both are 100 W, the spotlight appears brighter because it concentrates the light in one direction. In this direction, the spotlight effectively appears to be emitting more than 100 W. In other directions, there is almost no light emitted by the spotlight and it effectively appears to be much less than 100 W.

4 Even if one of the antennas is pointed in the general direction of the university, the antenna beam would be thousands of meters above the university.

References

Environmental Protection Agency. An investigation of microwave and radiofrequency radiation levels in Vernon, New Jersey, November 10-16, 1985. EPA; June 1986.

Institute of Electrical and Electronics Engineers. Standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3 kHz to 300 GHz. C95.1-2005. IEEE; 2005. Available at: https://standards.ieee.org/findstds/standard/C95.1-2005.html; accessed 31 March 2017.

International Commission on Non-Ionizing Radiation Protection. Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz). Health Phys 74(4):494–522; April 1998.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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