We designed a common source antenna array for the pavement inspection by ground penetrating radar (GPR). The antenna array consists of six Vivaldi antennas, one for the transmitter and five for the receivers. We calibrated the employed Vivaldi antenna array by considering the antenna phase center position. The time delay of electromagnetic waves from the antenna feeding point to the point of incident on the ground surface is compensated according to the antenna offset and the estimated phase center position. The results of the laboratory measurements demonstrated that the phase center calibration can greatly improve the accuracy of velocity and thickness estimations. A field measurement on a highway pavement indicate that error of the thickness estimation of the asphalt layer is less than 6 mm (10%). We conclude that the developed GPR technique can take an important role in the non-destructive testing of civil engineering structures.