PORTLAND, Ore. — Compact antennas are usually one-quarter the length of the wavelength being transmitted, but Virgina Tech engineers are claiming a 2.5-fold reduction in the size of an ultrawideband antenna.

The compact UWB antenna (CUA) has a curved multi-element shape twisting around the inside of a spherical shape with a diameter just one-tenth that of the wavelength being transmitted.

"We needed to know how to build an UWB antenna that came close to the size limit, and the CUA invention has accomplished this by fully utilizing the volume of a specified diameter," said Virginia Tech engineering professor Warren Stutzman.

The CUA's shape seems to extend along the length of individual antenna elements, longer than its diameter appears, then twisting around the inside of its radome, or protective housing.

Virginia Tech's compact ultrawideband antenna fully uilizes the volume inside its protective housing (not shown).

According to Yang, the antenna achieves nearly optimal UWB performance for low energy, short-range transmissions of high-bandwidth data such as video signals. Other 10:1 bandwidth antennas exist, such as spiral and log-periodic designs, but Yang claimed those do not work well in radar applications. The CUA, according to Yang, will work in pulsed radar systems.

The key to the CUA is how it makes use of a spherical volume to pull in nearly the maximum amount of signal power that is theoretically possible.

Instead of conventional AM, FM or similar encoding schemes, UWB uses pulsed transmissions that encode information by generating radio energy at specific times over large bandwidths. The technique is called pulse position or time modulation.

The CUA harnesses the theory underlying UWB antennas by employing arms that wrap around a metallic central core that maintains a relatively constant distance from the arms. The design could be etched on the inside of a radome in low-cast applications, or could be constructed from curved wires or tubing.

"This antenna has a 10-to-1 instantaneous bandwidth," said Yang. "It could be used for frequency domain, multiband, multichannel applications, as well as for time-domain or pulsed applications."

Typical 10:1 bandwidth antenna designs, such as spirals, will not work in pulsed radar applications, according to Yang, because they do not maintain even group velocities across their entire band. The CUA, however, overcomes group velocity limitations by making better use of an entire 3-D space inside the radome rather than just a flat planar area.