In this study, the standard methods of monopole antenna calibration are interrogated and the use of alternative methods is investigated. For this purpose, the GTEM cell has been used for two standard identical monopole antenna calibrations. The dummy antenna (approximate to 10pF by ANSI, approximate to 12pF by CISPR), which is suggested as standard methods in ANSI C.63.5 and CISPR 16.1.4 are not appropriate to simulate the actual monopole. So Manufacture Antenna Simulator (MAS) has been used as an alternative equivalent circuit substitution method (ECISM) of the rod. Good agreement between GTEM measurement and ECISM is observed. Calibrations with standard and alternative methods are performed and the reliability of these methods is discussed in the frame of the measurement results.