The ground penetrating radars (GPR) are increasingly finding application in several disciplines, including geotechnical site investigations, for rapid non-invasive utility mapping. A critical factor in determining the depth of exploration and resolution of a GPR is its frequency. Every GPR has a nominal frequency. However, two GPRs with same nominal frequencies may vary in their center frequencies. The emitted pulses from the transmitting antennas are attenuated by the medium before being reflected back and received by the receiver antennas. Efficient processing of the reflected wavelets requires knowledge of the antenna characteristics mainly their center frequency, temporal length and shape and their effect on the reflected wavelets. This paper outlines an attempt at determining the characteristics of an impulse type 400 MHz GSSI antenna and evaluating their impact on utility mapping. Experimental studies have been carried out under controlled conditions, which involved scanning metallic pipes of different materials and sizes. Direct and reflected waves in air are gathered and the signals obtained are processed in the time and frequency domains. The former gives information about the signal characteristics and the latter, the frequency content. The results show that the true center frequency of the antenna is 310 MHz. The temporal length is 2.8 ns. Vertical and horizontal resolution of buried pipes is an important factor in utility mapping. GPR data for vertical resolution of a pair of GI pipes is collected and role of antenna characteristics is evaluated.