In this thesis, a reflection-type three antenna method is to combine the concepts of three antenna method and antenna scattering matrix to measure the antenna gain and its structural scattering characteristics. The path lengths between the transmitting and receiving antennas can be calculated from the measured data at two different distances. In the measurement, a man-machine interface is written in Visual Basic language to record the measured data from the VNA, then each antenna gain and its structural scattering characteristics can be calculated from the measured data. In addition, the measurement results are compared with the results using the transmission-type three antenna method.