Circuit modeling methodology for UWB omnidirectional small antennas

In ultra-wideband (UWB) systems, antennas act as filters that introduce a frequency dependent response from the transmitter to receiver. To capture the waveform dispersion so that one can equalize/compensate at the transmitter/receiver, a new circuit modeling methodology that handles omnidirectional small antennas is proposed. By transforming the antennas into the degenerated Foster canonical forms and utilizing the waveform-omnidirectional property, it is shown that the transmitted far field waveform is a scaled version of the voltage across the radiation resistor in the model. Extended Thevenin/Norton equivalent circuits with dependent sources tracking the frequency dependence of the antenna effective length are also built for UWB receiving antennas. Simulation and experimental results show that this methodology is effective over a wide bandwidth and suitable for modeling most UWB antennas.