Adaptive Antennas

Correcting the myths surrounding the correction factor

Adaptive antenna array systems transmit targeted signals to active end devices such as smartphones or laptops. Very little radiation is emitted in other directions, which significantly reduces total exposure. Because the assessment methods used do not take this into account, only a correction factor permits equal treatment with conventional antenna systems. Critics of mobile technology consider this a scandalous relaxation of the limits.

By Michael Lieberherr
Two people on the terrace

Let us use sound as an analogy for radiation: adaptive antennas ‘speak’, or transmit, directly to the end device. The ambient sound level is low and does not disturb anyone who does not want to actively listen. The overall noise volume is thus greatly reduced. Conventional antenna systems, on the other hand, blast the entire radio cell evenly, generating a comparatively high ‘noise level’ for everyone, both mobile phone users and non-users.

Using the existing assessment method, which is based on the even, static transmission characteristics of previous antennas, the radiation of adaptive antennas is massively overestimated (see diagram). This assessment method also dates back to a time when all you could do with a mobile phone was make phone calls, send text messages or play Snake in black and green on a Nokia.

Infografik zu adaptiven Antennen

Fairer assessment thanks to correction factor

With the introduction of the assessment method adapted for adaptive antennas, the Federal Office for the Environment (FOEN) clearly stated that it was not about giving an advantage to the latest generation of antennas, but about eliminating a disadvantage compared to conventional antennas. The requirements have thus been adapted to the current state of technology. To remedy the above-mentioned overestimation situation, the exposure assessment of adaptive antennas may now be performed using a correction factor.

This ensures the same ‘rigour’ as that used in the exposure assessments of conventional antennas. Thus, contrary to what critics may repeatedly allege, total exposure from the adaptive antenna is no higher than that from its conventional counterpart (see diagram). The Federal Office of Communications (OFCOM) corroborates this.

Contrary to numerous claims, the correction factor does not allow the limit value to be exceeded. It prevents an excessively tough assessment of the effective exposure.

Infografik zu adaptiven Antennen

The correction factor may locally, in a place of sensitive use, and for an extremely short period, result in the extrapolation of field intensities in excess of 5 V/m (see green area in the right-hand graphic). Averaged over 6 minutes, the stringent precautionary installation limit value, which has been in place unchanged for 20 years, must be adhered to at all times, however. Due to the extremely dynamic way in which adaptive antennas work, this is automatically the case in 95 to 98% of use cases owing to statistical distribution. To ensure that the precautionary value is always adhered to even in the remaining cases, validated software continuously monitors the radiated power of the antenna. This automatic power control provides additional quality assurance and guarantees the lawful and compliant operation of all installations.

In other words, adaptive antenna array systems also comply with the extremely stringent installation limit value at all times, as Federal Councillor Sommaruga, Head of the Federal Department of Environment, Transport, Energy and Communications, explained to the media. The installation limit value is now also averaged over time, as has always been the case with the ten times less stringent exposure limit value. The exposure limit value applies to places where people remain for only a short period of time.

Not a free pass

Returning to the very brief power spikes of adaptive antennas. Critics see in this a massive relaxation of the extremely stringent Swiss precautionary values. The physicist explains: The theoretical maximum exposure from one of our adaptive antennas is just below 19 volts per meter. In reality, however, this does not happen and even the much lower power spikes occur, at most, within a few fractions of a second to seconds at most.

So is it in the interest of a network operator to even come close to this theoretical maximum? No, of course not. Because, if it did, the antenna would only be permitted to transmit at full power for 36 seconds, but would then have to switch off completely for 5 minutes and 24 seconds in order to maintain the 6-minute average.

Imagine that at Zurich train station: optimum data connection for 36 seconds, followed by a break of transmission of 5 minutes and 24 seconds for hundreds of users? Calls would also be interrupted after 36 seconds. For practical reasons, it is in the operator’s interest to distribute power as evenly as possible. The 19 volts per meter figure remains hypothetical and is far from a relaxation of the current limits.

Terms

Installation limit value:

Applies in places of sensitive use and is ten times more stringent that the international limit values. The installation limit value in this form applies only in Switzerland. It is unknown in other countries.

Exposure limit value:

Based on international standards and has always applied in Switzerland in places where people remain for only short periods.

Places of sensitive use (sensitive locations):

Places where people regularly remain for longer periods.

Examples of sensitive locations:

  • Domestic homes (and holiday homes)
  • Classrooms and nurseries
  • Patients’ rooms in hospitals, retirement and care homes
  • Hotel rooms
  • Permanent workplaces
  • Children’s playgrounds (if stipulated by spatial planning law)
  • School yards and nursery play areas, if used as children’s playgrounds
  • Land zoned for building

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