Abstract: The oscillating voltage signal on the antenna terminal and the electric field at far-field district are analyzed by equivalent circuit and commercial electromagnetic software, respectively, taking monocone and helical antennas for examples. It is demonstrated that the center frequencies of the generated electromagnetic pulses coincide with the characteristic frequency of the switched oscillator adopting either element antenna with the same electrical length as the switched oscillator (electrical length matched) or traveling wave antenna. However, there are some differences between them. For an element antenna (electrical length matched), the duration of the output pulse is relatively short with low Q value and the energy disperses in a relatively wide band in frequency domain. On the contrary, the duration of the output pulse is relatively long with high Q value and the energy concentrates on a relatively narrow band in frequency domain for element antenna. This result helps to understand the generation of high power electromagnetic pulse utilizing switched oscillator and has practical significance to the antenna choice in different application occasions.