**5. Conclusions**

The effects of small ground-plane sizes of planar UWB monopole antennas and feeding cable on measurements have been described and studied using computer simulation and measurement. A group of nine UWB antennas with the same radiator but different ground-plane sizes have been used for studies. Results have shown that the widths of the ground planes have more effects on the measured efficiencies. There are large discrepancies between the simulation and measured performances of these antennas at low frequencies.

The models of two practical feeding cables have been developed for studying the cable effects using computer simulation. Measurement results have verified the accuracies the two simulation models. Both the simulation and measured results have shown the feeding cable without EMI suppressant tubing has significant effects on measurements.
