A class of ultra-wideband miniaturized traveling-wave (TW) antennas comprising a conducting ground surface at the base, a plurality of TW structures having at least one ultra-wideband low-profile two-dimensional (2-D) surface-mode TW structure, a frequency-selective coupler placed between adjacent TW structures, and a feed network. In one embodiment, a 2-D surface-mode TW structure is positioned above the conducting ground surface, a normal-mode TW structure placed on top with an external frequency-selective coupler placed in between; continuous octaval bandwidth of 14:1 and size reduction by a factor of 3 to 5 are achievable. In other embodiments using at least two 2-D TW structures and a dual-band feed network, a continuous bandwidth over 100:1, and up to 140:1 or more, is reachable. In yet another embodiment, ultra-wideband multi-band performance over an octaval operating bandwidth up to 2000:1 or more is feasible.