Abstract In this thesis, the antenna gain and phase center are calculated from a set of S21 measurements at two different distances using the three-antenna method and the multi-antenna method. By using the three-antenna method and the S21 measurement in a reflection-type RCS arrangement, the phase center of antenna is measured and verified as a frequency dependent value. In addition, the path lengths between the transmitting and receiving antennas can be calculated from a set of S21 measurements, the measured antenna gain using three-antenna method given in Chapter 4 is shown to be accurate and distance independent. The approach of multi-antenna method is then presented in Chapter 5 with experimental results to measure the antenna gain and phase center of the test antennas in a cost-effective manner.