An important factor for the precise interpretation of ground penetrating radar (GPR) records is to know as much as possible about the transmission features of our antennas. The accuracy of the retrieved parameters in the GPR data inversion depends on the accuracy of the GPR external calibration. In this paper we studied the calibration technique for step frequency continuous wave (SFCW) GPR by two different methods namely, calibration by averaging and calibration by using linear transfer function (LTF) model. The SFCW GPR is implemented with the help of a vector network analyzer (VNA: E50715 of Agilent) and 0.8-4.5 GHz single TEM horn antenna. GPR system using their antenna is calibrated several times at different heights over a metal plate. The error in the calibration based on inaccurate antenna height over metal plate. © 2017 IEEE.