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 t he potential for harmonious coexistence between ISM (industrial, scien tific and medical) equipment operating within or outside the 900MHz IS M bands (896 and 915MHz) and cellular radio systems. The equipment pri marily under consideration has been high-power magnetron-based microwa ve heating equipment, and the effects on both analogue and digital cel lular systems have been assessed (Kenington and Bennett, 1993). The pr evious work has been concerned with the protection ratio afforded to t hese cellular systems by accurately simulated ISM signals, generated i n a laboratory environment. The authors describe the final phase of th e work, which involved performing field measurements around a number o f 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 o f potentially poor cellular reception, based on the previously derived protection ratios and assumptions about the location of the nearest b ase station. This work has been carried out, in part, to help explain the very low number of incidences of interference between ISM equipmen t and cellular radio equipment, despite the high emission limits set f or this equipment in the UK (120dB mu V/m at 30m from the wall of the building housing the equipment).