Ground-Penetrating Radar (GPR) is a non-destructive geophysical method applied in many civil engineering applications. The knowledge of the GPR antennas behavior is crucial to obtain accurate results and comprehensive data interpretations. However, the age of the antennas and the use can modify the values provided by manufacturers. Consequently, calibration of antennas is recommended. Calibration involves determining several parameters. In this paper, the evaluation of two parameters (stability of the signal and zero-time position) and the analysis of the effects of stacking are presented. Three antennas characterized by nominal center frequencies of 500 MHz, 800 MHz and 1.6 GHz are analyzed. The direct wave was used for the stability analysis in two propagation media: air and concrete. The results of the stability evaluation seems to indicate that the emitted signal and the reconstruction of A-scans are quite stable and noise as consequence of electronic noise is low. Zero time position was measured in air, calculating the propagation time for the reflection on a metallic surface. © 2018 IEEE.