High-frequency antennas transmit radio waves across vast distances and even over mountain ranges using very little energy, making them ideal for military communications. These devices, however, have one big problem: They need to be huge to operate efficiently.
Instead of adding more bulk, University of Wisconsin–Madison engineers are working to increase the effective size of antennas by turning the military vehicles that carry them into transmitters—using the structures that support the antennas themselves to help broadcast signals.
Troops in remote locations need to communicate by radio and move quickly, unencumbered by heavy and unwieldy equipment. However, antennas need to be at least one-quarter the length of the radio waves they transmit in order to operate efficiently. High-frequency military signals use radio waves ranging from roughly a football field in length to the distance of a successful first down—10 yards. Even at the small end, the ideal size for an antenna is taller than an average adult.
“Unsurprisingly, we don’t use antennas that are that big,” says Nader Behdad, an associate professor and Harvey D. Spangler Faculty Scholar in electrical and computer engineering at UW–Madison. “Putting a big, long antenna on top of an amphibious assault vehicle would be too high-profile.”
Short antennas lighten loads at steep costs to performance. The devices are inefficient, dissipating as much as 90 percent of input power as useless heat instead of useful broadcast radio signals.
“The problem is that antennas that are a small fraction of the wavelength can’t really communicate over long distances, and data rates cannot be as fast as they should be,” says Behdad.
Increasing the size of an antenna without adding to its physical dimensions sounds impossible. However, real-world military antennas are almost always attached to other things—for example, large, metallic objects like trucks and armored transport or amphibious assault vehicles—and Behdad realized that these structures themselves could broadcast radio signals.
“We are proposing to use the platform itself as the antenna,” says Behdad, whose research is supported by a $550,000 grant from the U.S. Office of Naval Research. “It’s a clever way to go around the limitations set by the laws of physics. From a practical point of view, the volume of the object on the military platform is the same, but we’ve effectively achieved a larger antenna.”