Electric field probes with three orthogonal elements were calibrated from 1-6GHz by the standard field method in an anechoic chamber. A special jig was constructed for setting and calibrating a Δ-beam-type probe. Calibration factors of the probes were obtained for each element using this jig. To reflect the future revision of IEC 61000-4 series, uncertainty in the calibration factors was investigated to improve calibration quality and determine the factors affecting calibration. We found that fluctuation in the power transmitted from a high power amplifier and the imperfection of the anechoic chamber were the most important factors affecting uncertainty.