An ultra-wideband loop antenna is proposed that is based on a wavelength loop antenna and a slot antenna. The self-complementary principle is applied to the designed ultra-wideband antenna. The antenna operates as a loop antenna in the low frequency band (0.3-1-GHz) and as a slot antenna in the high frequency band (1-14.2-GHz). The measured -10-dB bandwidth is 47.3:1 (0.3-14.2-GHz), and the size of the antenna is 220(0.22- L )×220(0.22× L )×177(0.18× L ) mm 3 , where λ L is the wavelength of 0.3 GHz.