Army Researchers Focus on Smart, Stealthy Antennas
If U.S. Army scientists have their way, future antennas for vehicles and dismounted infantry will be smaller and more nondescript and will feature greatly increased reception. Research is focusing on lightweight conformal antennas that can be built into soldiers’ uniforms and equipment as well as vehicle structures.
One of the major thrusts of the Army’s work is making antennas less obvious, says Dr. Steven Weiss, team leader of the U.S. Army Research Laboratory’s (ARL’s) antenna team. He notes that Army researchers also are examining new technologies such as metamaterials—engineered substances that do not have properties found in nature. For example, mounting antennas to conform to the side or the inside of a vehicle can affect their performance, but antennas made of metamaterials may counteract some of these effects.
The Army is interested in developing conformal antennas for ground vehicles. These could be used for communications or jamming improvised explosive devices. Because they are part of the vehicle’s structure, they lower its overall visual profile, making it more survivable on the battlefield. Antennas could be inconspicuously mounted onto vehicles in a number of ways: flush against the vehicle’s skin, incorporated into part of its structure such as a bumper, or conformed to the contours of the vehicle’s shape.
But developing conformal antennas for ground vehicles presents a variety of challenges. These issues include ground effects, such as radio interference, and size and weight issues for vehicles equipped with the antennas.
Weiss notes that researchers want to develop electronically scannable antennas that do not move physically but would enable radios to maintain point-to-point communications. Electronically scanned phased antennas are used for radar systems on ships and aircraft, but their cost prohibits mass installation on ground vehicles, he says.
The Army has a pressing need for antennas that provide data and satellite communications on the move. Weiss cites the ARL’s satellite communications on-the-move effort as an example of the service’s research goals and challenges. “How do you replace a double gimbaled dish antenna with a phased array that is not a budget buster or requires a refrigeration system to keep the antenna cool?” he asks. Another criteria is the ability to support enough bandwidth to manage multiple communications functions.
In addition, ARL scientists are examining metamaterials for new antenna applications. Weiss cautions that there was a great deal of hype about metamaterials when their potential was first developed but adds that they can be effective for work on conformal vehicle antennas. He notes that researchers are interested in one particular type of application known as artificial magnetic conductors (AMCs).
When an AMC is placed between an antenna, such as a dipole antenna, and the metallic roof of a vehicle, the AMC allows the antenna to radiate broadside, out of the vehicle. Without an AMC, the antenna would short out and not radiate in the desired direction, he says. He cautions that AMCs for dipole antennas are somewhat limited in bandwidth but adds that this capability was not even available 15 years ago.
Steel armor isn’t the only material that can interfere with radio communications. Weiss says that ceramic armor also has its own set of challenges. He notes that an AMC would be helpful to get signals through ceramic composite armor. Ceramic armor does not short out an antenna, but it creates additional load on transmissions and limits a radio’s bandwidth, he says.
For communications on the move, ARL researchers are interested in Rotman Lens beam formers. These are compact devices used to focus microwave communications transmissions. Weiss says that Rotman Lens-based antennas could be installed on all four sides of a vehicle. These antennas are about one foot to 18 inches across and fractions of an inch thick, allowing them to be easily mounted on vehicles.
This antenna, which operates in the C band, currently is being prepared for field tests. “To our knowledge, no one has made a Rotman Lens that’s flexible. Ours is made of such a thin material that we could put the lens flush to the roof and then bend it around the corner so that the antenna array is pointing out to the side, and we wouldn’t need as much surface area on the side,” he says. If the beam-forming antenna is suitable for operational use, Weiss explains that the technology will be handed over to the U.S. Army’s Communications-Electronics Research, Development and Engineering Center (CERDEC) and prepared for mass production.
Another promising technology is micro electromechanical system (MEMS) radio frequency phase shifters. Weiss notes that the ARL has purchased MEMS phase shifters from Raytheon Corporation and made small demonstrator array modules operating in the K band at 30 gigahertz for satellite communications on-the-move applications. He cautions that this technology is not ready for operational use but adds that it has matured considerably over the past decade.
Weiss notes that the holy grail of antenna research for ground and man-portable systems is a single antenna capable of transmitting across all required military frequencies. “We’re not going to get a shared aperture that does everything, but we might get a shared aperture that does two or three things, and then another shared aperture in another frequency band that does two or three things,” he says.