Compact UWB antenna extends bandwidth to radars

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

Compact antennas are usually one-quarter the length of the wavelength being transmitted, but Virginia Tech Inc. engineers are claiming a 2.5-fold reduction in the size of an UWB 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 Warren Stutzman, engineering professor, Virginia Tech.

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.

According to Virginia Tech, 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, the company said, 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 has 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 Taeyoung Yang, inventor of the technology. "It could be used for frequency domain, multiband, multichannel applications, as well as for time-domain or pulsed applications," he added.

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 3D space inside the radome rather than a flat planar area.

- R. Colin Johnson
EE Times

Keywords: UWB   antenna   video signal   radar system