Measurement and simulation of radiofrequency emissions from telecommunications transmitters

Phillip Knipe

Significant concern has been expressed regarding the potential link between various health problems (eg cancer) and exposure to radiofrequency (RF) electromagnetic energy (EME). In particular mobile phone base stations, commonly referred to as radio base stations (RBS) have attracted public attention. With the number of these RBS increasing around the world, questions have been raised about the fields generated by these types of equipment. In particular the public and the industry are interested in the strengths of these fields and how they compare to the regulatory standards of various countries. There are two approaches that can be used to determine the field strengths generated by the RF EME transmitting installations. They can be physically measured using expensive and sophisticated equipment, requiring a significant level of technical knowledge, or alternatively, they can be modelled theoretically using complex simulations. Due to the number of installations that already exist, and the rate at which their numbers are increasing, the physical measurement of these sites may be considered impractical and expensive. Therefore, simulation of the RF EME fields from these installations is often the preferred option. In Australia, the industry code C564:2011 – Mobile Phone Base Station Deployment (CA 2011) ‐ requires that site RF EME assessments for Mobile Phone Radiocommunications Infrastructure must be completed in accordance with the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) prediction methodology Technical Report – Radio Frequency EME Exposure Levels – Prediction Methodologies (Bangay 2002). The purpose of the assessments is to provide affected persons in the community with a reliable, objective and near worst case, line‐of‐sight estimate of the maximum levels of RF EME likely to be emitted by the proposed or upgraded mobile phone base station installation, for full‐power operation without producing a gross over‐estimate (CA 2011). The aim of this study is to test, using actual field measurements, whether the assumptions made in the ARPANSA prediction methodology result in achieving the stated purpose of the assessments as explained above. This study compares the calculated RF EME levels by a number of commercial software packages, for a number of service providers and technology types (i.e. WCDMA850, GSM900 and 1800 and UMTS2100), at a number of locations, to the measured levels for those same locations. As part of the measurement component of this study the applicability of a number of spatial averaging assessment techniques will also be considered. In particular the 3, 6 and 9 point spatial averaging techniques recommended in the IEC assessment standard and a 7 point spatial averaging technique, recommended by the Australian Radiation Protection Agency (ARPANSA) are compared and evaluated. The main findings of this study are: 1. Overall, the ARPANSA prediction methodology does achieve its stated purpose. 2. The largest overestimation of the RF EME levels by simulation was 20.92 dB (124 times). Whilst, this appears to be quite large the largest simulated level was 624 times below the general public limit. 3. The use of a single measurement point to determine RF EME levels for a given location could result in an under estimation of the levels beyond the ±3 dB uncertainity of the measurements (‐8.18 dB). If completing measurements to confirm compliance to the regulatory limits it would be better to use the 9 pt averaging technique when the 1pt measured level is greater than 30% of the applicable limit. 4. Comparisons between the measurement and simulation results revealed that they do not always closely align with each other. However, in all cases where this occurred, the simulated levels did not under estimate the measured levels by more than 0.82 dB beyond the combined uncertainty of the measurements and simulations.

Measurement and simulation of radiofrequency emissions from telecommunications transmitters

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