Ultra-WideBand Antenna Array Systems

(source: Novel planar design enables ultra wideband phased array antennas, by Ashok Bindra, Editorial Director )

Conventional phased array antennas used in military systems are large and bulky. To alleviate this problem, researchers at the Georgia Tech Research Institute (GTRI) have developed a new approach to phased-array antenna design. As a result, a single ultra-wideband antenna is now capable of doing the job of five conventional antennas. For that, the GTRI researchers have combined the benefits of fragmented aperture antennas in a computer-designed planar system with mutual coupling between antenna elements. As a result, the researchers have demonstrated a 300 MHz to 10 GHz (33-to-1) bandwidth - well beyond the 10-to-1 ratio achieved by conventional designs. But, the ultimate goal is to extend that range to 100-to-1 for use in radar and communication applications.

"Instead of trying to avoid mutual coupling, we designed it into the antenna where it actually provides a lot of benefits – including allowing us to have an extremely wide bandwidth," explained Jim Maloney, a principal research engineer at GTRI’s Signature Technology Lab (STL) principal research engineer. "What everybody used to avoid was actually the silver bullet that makes this work."

"Phased array antennas take up space, and if you must have a different antenna for every function - communications, radar and other tasks - the space required can be considerable," noted Paul Friederich, a principal research engineer in STL. "On any military platform, space is at a premium.” Current ships must carry dozens of antennas - a problem for all ships, especially submarines. Aircraft have limited surface area for antennas, with weight always a concern. Ground vehicles and even individual soldiers could benefit from reducing the number of antennas they must carry, Friederich noted.

Because it is flat and can be conformed to surfaces, the new antenna design could also have commercial applications, added Friederich.

Beyond potential use on military aircraft, ships and ground vehicles, the technology developed in STL could also have applications for devices that would not need broad bandwidth - such as wearable antennas that could be incorporated into military uniforms or even tents. The conformal nature of the devices could also open up commercial applications, though cost could be an obstacle, according to the researchers..

"Now that we have shown the antenna works, we are in a consolidation phase of work in which we're trying to figure out which bandwidths make sense for particular applications, and we working with corporate partners to the design the electronics that will be needed," added Friederich. "It's just a matter of time before we see these antennas begin appearing on military platforms."

The 33-to-1 antennas are flat and include three layers of metal foil fabricated in computer-designed patterns using printed circuit board technology. A prototype that works down to 300 MHz is 16 inches square and about three inches thick - providing a substantial size, weight and volume savings over conventional "egg crate" antennas.

Beyond their circuitry pattern, the antennas also need a backplane to reflect electromagnetic energy - and protect the electronic control equipment behind the antenna. The new antenna also relies on computer-designed innovations: a broadband screen "backplane" made up of foam and partially-conductive films.

"We had to make a new backplane that would be compatible with the extreme bandwidths so it wouldn't degrade the antenna performance, so we developed a laminate of foam and partially-conducting layers to do that in an optimal way, explained Friederich."

Testing the antenna performance was also not a trivial task. Conventional antenna test systems were not sufficient. Hence, the researchers had to evaluate their 33-to-1 device in three different antenna test facilities to cover the entire frequency range.

GTRI has been working on the ultra wideband antenna for nearly a decade, building new technology on top of detailed computer models. “Nobody could really study the mutual coupling effects until computers became good enough to evaluate what would happen when you moved elements around and changed their shapes in the presence of other elements," stated Maloney. "One of our strengths is an ability to do very detailed and accurate numerical models of antenna performance. We can determine how antennas are going to perform without having to build them."

By simplifying construction of the radiating structures, the antenna electronics become the driver of the overall cost. Long term savings there will depend on advances in microelectronics fabrication, Friederich cautioned.