Three antenna systems, composed of circular monopoles with different ground plane sizes, are studied. The transmission of an UWB pulse between two identical monopoles is analyzed. The omnidirectional properties of the UWB antennas are measured and simulated in frequency and time. The System Fidelity Factor of each system is obtained, quantifying the distortion of the received pulses in the azimuth plane. Results show that. the size of the ground plane affects the efficiency of a monopole system when transmitting an UWB pulse.