Gain measurements of ultra-wideband antennas often require the use of a broadband reference antenna, typically a horn antenna. Since this type of measurement is commonly performed over a short range, it is essential to not only accurately know the gain of the reference antenna but also the position of phase center as a function of frequency. The technique proposed in this presentation requires just six S/sub 21/ measurements with three antennas to accurately determine the gain and the phase center of each antenna and is a significant saving in time and resources compared to conventional phase center measurements.