A comparison between a cavity backed spiral and a resonant monopole - an ultra-wideband consideration

The impulse response waveform of a cavity-backed spiral shows significant ringing and slow decay, making it unsuitable for ultra-wideband applications. However, the resonant monopole and its relatives, considered to be narrowband antennas, are potential ultra-wideband radiators. The monopole offers little dispersion with a typically fast decay of a ringing sinusoid. The fast decay creates the effect of a short pulse. Thus the monopole is a potentially good UWB antenna, though the efficiency may produce less than an optimal pulse amplitude.