Whitepaper
What is Antenna Factor?
This Com-Power application note (AN-107) offers a conceptual and technical exploration of antenna factor for EMC engineers. It defines antenna factor as the ratio of the electric field strength surrounding an antenna to the voltage induced at its output terminals, expressed in dB microvolts per meter. The document explains why the concept is so widely used in EMI testing — its linearity at any given frequency makes it a simple additive correction — while also laying out the practical limitations engineers must keep in mind. These include the assumption of a uniform field (rarely met in practice), the dependence of antenna factor on calibration distance, the importance of careful handling and regular calibration verification, the need to ensure active antennas remain in their linear range, and the impact of impedance mismatch (VSWR) on voltage readings. The note closes with the mathematical derivation linking antenna gain to antenna factor, yielding the expression AF = 9.7 / (λ√G).