A balloon-shaped ultrawideband (UWB) antenna is developed, and its scattering characteristics are theoretically and experimentally studied in both the frequency and time domain. The radar cross-section (RCS) and scattering waveforms of the UWB antenna terminated with three different kinds of loads are simulated and measured. The results which are in good agreement show that, the balloon-shaped antenna is with almost omnidirectional scattering pattern, and its scattering of antenna mode and structural mode are obviously separated in the time domain. Therefore, this antenna is an eligible candidate for the passive ultrawideband-enabled radio-frequency identification (UWB-RFID) tag applications. Furthermore, the scattering waveform of this antenna is valuable to clarify the differences on the definitions of structural and antenna modes.