Absolute Measurements for Small Loop Antennas for RF Magnetic Field Standards

A method to determine accurately the strength of magnetic fields produced by a transmitting small loop antenna for the RF field standards is presented. The field strength can be determined by the magnetic dipole moment of the loop. A loop antenna factor is introduced to express the magnetic dipole moment of a transmitting small loop antenna in terms of the incident power to the antenna input port. The emergent power from the output port of a receiving small loop antenna can also be expressed in terms of the magnetic field to be detected and of the loop antenna factor. The insertion loss method (or the three antenna method) is applied to measuring the loop antenna factor. Small loop antennas with diameters 10 cm were designed, and loop antenna factors were measured by the insertion loss method over frequencies up to 30 MHz with a systematic error of 0.08 dB.