Calibration of circular loop antennas

The calibration of a measuring loop antenna means assigning an antenna factor K for each frequency in the entire measurement band. Such a loop antenna factor can be found either by calculating the impedances of the loop, or by using a well-defined standard magnetic field of a transmitting antenna. For both methods, it is necessary to obtain an accurate relation between the magnetic field and the geometrical dimensions of the loops. Generally, a manufactured loop has a complex geometric shape with complex electrical behavior so that its impedances cannot be accurately determined. The standard magnetic field method must then be used for traceability of the calibration. The necessary expressions, taking into account the dimensions of the loops with finite conductor radii including the current distribution along the loop, are given. Greene's equations are accurately calculated with mathematics software on a personal computer for the near-zone as standard average magnetic field. With the procedure presented here, the calibration is reduced to an accurate measurement of attenuation.