Field measurements study into the potential effects of ISM emissions on cellular radio equipment

A study has been under way in the UK for a number of years examining the potential for harmonious coexistence between ISM (industrial, scientific and medical) equipment operating within or outside the 900 MHz ISM bands (896 and 915 MHz) and cellular radio systems. The equipment primarily under consideration has been high-power magnetron-based microwave heating equipment, and the effects on both analogue and digital cellular systems have been assessed (Kenington and Bennett, 1993). The previous work has been concerned with the protection ratio afforded to these cellular systems by accurately simulated ISM signals, generated in a laboratory environment. The authors describe the final phase of the work, which involved performing field measurements around a number of different ISM installations in widely differing locations around the UK. These measurements were performed to assess the current levels of emissions from ISM equipment and the form of the `radiation pattern´ of typical installations. From this it is possible to estimate areas of potentially poor cellular reception, based on the previously derived protection ratios and assumptions about the location of the nearest base station. This work has been carried out, in part, to help explain the very low number of incidences of interference between ISM equipment and cellular radio equipment, despite the high emission limits set for this equipment in the UK (120 dBμV/m at 30 m from the wall of the building housing the equipment)