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This paper proposes a simple, fast, and accurate method for calibrating the free-space antenna factors of broadband electromagnetic compatibility (EMC) antennas. This method adopts a fixed-height calibration configuration and a multiple-signal-classification-based (MUSIC) data processing algorithm. Because this configuration does not require height scans, it significantly shortens measurement time and removes height-dependent calibration errors. In addition, the MUSIC-based data processing algorithm can remove unexpected reflections from the ground plane or any other reflecting objects, and transfer calibration into the free-space transmission model, from which the free-space antenna factors are obtained. The algorithm of this method can also automatically compensate for the phase center shift, which makes measurement easier and more convenient. To verify this method, numerical simulations for half-wave dipoles and experimental measurements for log-periodic dipole array (LPDA) and horn antennas are conducted. The simulated results for the half-wave dipoles indicate that the error from the theoretical AFFS can be within ±0.5 dB. In the case of the experimental measurements, the calibrated results are compared with other published standard methods: the mean differences can be as low as 0.25 dB for the LPDA, and as low as 0.36 dB for the horn antennas. The good agreement between results confirms that the proposed method can yield accurate estimations of free-space antenna factors for broadband EMC antennas. This method also provides a new alternative for obtaining fast and accurate antenna calibration.