Basic characteristics of magnetic field antenna factor of loop antennas for EMI measurements

Abstract

For frequencies below 30MHz, electromagnetic interference (EMI) measurements are performed by measuring magnetic field components using a loop antenna. The field strength is given by the voltages read by an EMI receiver and the magnetic field antenna factor (MFAF) of the loop antenna. To measure the field strength accurately, the MFAF of the loop antenna is the most important parameter. In this paper, the basic characteristics of the MFAF of loop antennas for EMI measurements are described, especially its definition, height dependence above a metal ground plane, and directivity at frequencies below 30MHz.