Researchers Whip Up Antenna Technology
U.S. Army officials seek to replace the commonly used device.
For decades, the U.S. Army has relied on the ubiquitous whip antenna for an array of air and ground communications, but those antennas often interfere with one another and are plainly visible to enemy soldiers in search of a target. Now, service researchers are using a wide range of technologies that could begin replacing the pervasive whip, providing more efficient, effective and reliable combat communications. Options include antennas embedded with vehicle armor, transparent antennas integrated into windshields and smart antenna technology capable of determining the optimal direction to focus transmission power.
The rule of thumb on the battlefield is that the more antennas sticking off of a vehicle, the more likely the vehicle is a high-value target with a high-ranking occupant. But this situation could change as officials at the Communications-Electronics Research, Development and Engineering Center (CERDEC), Aberdeen Proving Ground, Maryland, investigate technologies for short- and long-term replacements for whip antennas, whether for dismounted, mounted or airborne communications.
“The antenna is the intermediary between the radio and the network. You can have a state-of-the-art radio and a very substantive network, but if you don’t have the antenna, the whole thing falls apart,” says Mahbub Hoque, acting director of CERDEC’s Space and Terrestrial Communications Directorate. “We have programs in this directorate—in the antenna division—starting from basic research to develop prototypes to technology ready to transition to the program managers and program executive officers.”
One of the short-term solutions included providing suggestions for dismounted soldiers crafting serpentine antennas to replace their whips, explains Mike Breckenridge, program manager for the Smart Distributed Antenna Systems (SiDEwayS) technology development program. “The dismounted soldier out kicking down doors, doing his mission, has a long, one-meter whip sticking up above him. It obstructs his mobility. So, a soldier often times will take a wire, strip it down and solder an end to it so that it will connect to the radio, and then wind that through the back of his jacket or his rucksack, and that will be his antenna,” Breckenridge explains. The jury-rigged solution kills off communications range but improves the soldier’s mobility, survivability and lethality, Breckenridge states. CERDEC researchers quickly discovered that the way the serpentine antenna was being wound caused it to interfere with itself. The current that was riding on the antenna was going in opposing directions as the soldiers wound it up and down. “Instead, we told them to wind it side to side so that the energy will provide some sort of vertical polarization and they can communicate at longer distance.” For the longer term, CERDEC is searching for a conformal antenna solution through the Small Business Innovation Research program.
More seriously, the organization is searching for a way to protect Marines from electrocution when their whip antennas come into contact with overhead powerlines, which has happened on a few occasions in the combat theater. “What we’re looking at in the short term is a kind of coating—something like a shrink wrap tubing or a spray-on solution—that we can give to soldiers in kits and they can install on equipment they already have. So, if they do hit an overhead wire, it doesn’t arc. All they need is an insulation powerful enough to protect them so that they can hit overhead wires all day long,” Breckenridge points out. “This is the short-term, quick solution because to re-field thousands of antennas is not going to happen overnight. In the longer term, we can develop more rugged coating at the factory or something in the design to reduce the risk.”
Common whip antennas are omnidirectional, transmitting power equally in every direction, which is not necessarily efficient. One of CERDEC’s more important programs for warfighters, Mahbub asserts, will require an antenna smart enough to decide in which direction to transmit. The system relies on a cognitive engine. “This cognitive engine listens to the network and determines the best route to communicate, and then it dictates the antenna to move in that direction,” Mahbub explains. The system will increase transmission distance by at least three times and will be a mobile communications boom, he asserts. “This type of antenna will really be a breakthrough antenna for the network. We started this project last year. Right now, we are looking into software development, and then we will go into the hardware side,” he adds.
Furthermore, future warfighters could have transparent antennas made of the metamaterial graphene, built right into their vehicle windshields. Graphene looks like glass but acts like a metal, meaning it can easily conduct radio transmissions. The CERDEC officials concede that automobile companies have been integrating antennas into windshields for decades, but those antennas are only for radio receivers, not transmitters, and they are easily damaged. In this case, the material would have to be several inches thick and armor-strong. The trick is to ensure transmissions travel in only one direction. “For tactical communications, it needs to be able to radiate out from the vehicle, and it needs to dissipate heat and energy. How do we make the transparent antenna radiate not inside the vehicle but outside the vehicle to communicate,” Mahbub asks.
Future Army vehicles, such as the Ground Combat Vehicle, also could have antennas embedded underneath the armor. CERDEC’s Embedded Platform Antenna Systems program is exploring those options. “We have been looking into several aspects of that, but there are challenges we are working on,” Mahbub allows. “The armor has to be such that it does not block the radiation because it will be on top of the antenna. We have done appreciable research on that, and the results are very encouraging.” But the armor also might enhance future antenna capabilities. “We can use the armor material to our benefit at certain times. We can put certain materials behind it or in front of it to either improve or direct the energy where we need it and actually use the armor to our benefit,” Breckenridge adds. CERDEC works closely with future vehicle development teams, including the Ground Combat Vehicle program personnel, to ensure antenna technologies are considered from the very beginning, rather than being added as an afterthought. “They will be taking some of the technologies that we’ve developed and maturing them over the next year and transitioning them in fiscal year 2013,” Breckenridge reveals.
Another option is to build antennas into polymer materials. “If you can imagine a polymer, such as a glue or similar material, you can pour in these very fine particles, and depending on how much you pour in and what particle you use, you will be able to change how the material acts,” Breckenridge says.
Ground-based antennas are not CERDEC’s only focus, however. The Leap Ahead Aviation Antenna Technology program is exploring a range of options for airborne antennas, including those for unmanned aerial vehicles (UAVs). The transparent antenna used in windshields potentially could be made thinner and used for aircraft. One issue the Army faces is that antennas on the bottom of an unmanned aircraft, such as the Shadow, can be blocked by the landing gear wheel struts. In that case, material known as an artificial impedance surface can direct the energy around the fuselage and re-radiate to fill in gaps, Mahbub says. “We can wrap that wheel structure with an impedance surface where the surface current introduced by the radiation from the antenna re-radiates on the other side,” he explains. “The concept is unique but very challenging. We have been successful with a flat surface, but if you have a curved surface, there are still challenges.”
Also for the Shadow unmanned air vehicle, CERDEC is exploring ways to add a directional array—which usually is larger, more complex and heavier than whips—without having to lose any of the platform’s current intelligence, surveillance and reconnaissance payload. Researchers are looking at both half-duplex and full-duplex solutions. They have found that using monolithic microwave integrated circuits allows the integration of multiple components onto a single chip. “We flew a prototype in August on a surrogate aircraft, and we’re now taking the results of that and looking into continuing testing in 2013. It shows excellent promise,” Breckenridge asserts. He adds that the technology dramatically increases the Shadow’s range. “With smaller whip antennas, you only have a certain distance before you break that link. Now, you’re able to have this UAV flying farther out and communicating information back to the base. What we’re expecting is at least a four-times increase in range,” Breckenridge says. CERDEC officials say they hope they will transition the technology to the program manager for unmanned air systems by fiscal year 2013, and that it could be fielded before fiscal year 2015.
Potentially, both ground and air vehicles also could benefit from a nanomaterial technology known as sputtering. CERDEC officials compare it to the process used for tinting automobile windshields. In this case, sputtered metal is sprayed into ultrathin sheets of film, 500 sheets of which would be about one-quarter-inch thick. The material could be used for conformal antennas in vehicle cavities, such as wheel wells, where it would replace thicker, heavier materials. That will allow for smaller cavities, leaving more space for other necessities, including cables, fuel or room for soldiers.
The Future Vertical Lift, a yet-to-be-defined conceptual aircraft that could replace multiple aging helicopter platforms in the 2030 time frame, could benefit from sputtering technology. “We’re starting to get on some of the integrated product teams and work with the people developing the requirements. They’ve told us they want zero antennas sticking out of their platform. They want everything to be conformal into the platform,” Breckenridge reports.
Although CERDEC personnel work closely with universities, industry and military laboratories to develop antenna technologies, up to 80 percent of their work is done in-house. Mahbub estimates that half of the programs are based on lessons learned from the wars in Iraq and Afghanistan; the other half are to meet the Army’s future vision. “Our end goal is to provide sustained communications to the network. The mission is really to address the soldiers’ needs. That is what we are trying to do,” Mahbub says.
