SUMMARYTo determine the magnetic complex antenna factor of a shielded loop antenna with double feed sections for highfrequency magnetic field measurement, two methods that combine the characteristics of a 180° hybrid obtained by measurement with numerical calculations of the element section are studied. The magnetic complex antenna factors obtained by the proposed methods are compared with that obtained from measurement by the three-antenna method. It is shown that the computation methods proposed in this paper are useful if the characteristics of the 180° hybrid can be expressed in terms of Z parameters or Y parameters. It is demonstrated that the uncertainty of the phase appearing, as a problem in the three-antenna method, can be resolved.