Whitepaper
Use of Antenna Factors in EMI Measurements
This Com-Power application note (AN-106) explains the concept of antenna factor as it is used in EMI radiated electric field measurements. Antenna factor is defined as the ratio of the incident electromagnetic field to the voltage at the antenna connector, and in logarithmic terms it can simply be added to the receiver voltage reading to obtain the E-field in dBµV/m. The note walks through a full worked example incorporating preamplifier gain and cable loss into the calculation and presents a sample data table formatted as it would appear on an FCC Part 15 radiated emissions report. It also discusses the key limitation of the antenna factor concept — the assumption of a uniform incident field — and describes both the two-antenna and three-antenna calibration methods, noting that antenna factors can vary with calibration distance and that this must be accounted for to minimize measurement error.