An antenna is calibrated in an open-field test site (OFTS) and/or an anechoic chamber, which facilities themselves need calibration. The procedures for calibrated test sites (CALTS) are given in the CISPR and ANSI/IEEE standards. The characteristic parameter for calibrated test sites is the normalized site attenuation (NSA). Theoretical calculations and practical measurements of normalized site attenuation are first presented. Antenna-factor (AF) and/or absolute-gain measurement methods are then reviewed. Finally, an alternative antenna calibration approach is given in this tutorial.