The Friis equation is often used to determine the gain of antennas but assumes that far-field conditions are met. For limited antenna separations on the order of the Fraunhofer distance, its use requires a precise estimate of the amplitude centers of the antennas. Using a new antenna gain measurement technique, it is shown that the amplitude center can be very well estimated and that the measurement results can be used to confirm that far-field conditions are met. Moreover, reflections caused by scatterers are averaged since multiple measurements are performed. The presented method is particularly useful for anechoic chambers that are limited in size, such as small anechoic chambers for the characterization of, for instance, 5G millimeter-wave phased arrays.