The influence of nonuniformity of electric and magnetic fields on the calibration accuracy of dipole and loop antennas in field sources based on four-wire transmission lines is theoretically investigated. The paper proposes to take into account the influence of the nonuniformity of the electromagnetic field of a four-wire source when calibrating thin dipole and loop antennas using the equivalence coefficients. The use of these coefficients, taking into account the distributions of the field in the source and the current on the antenna conductors, can significantly weaken the requirement for field uniformity when calibrating antennas. For some common types of antennas, formulas are derived for the equivalence coefficients in the approximation of a four-wire source by an infinite line. Approximation formulas, simplified for engineering calculations, are obtained.
