A lot of chatter can go into planning a stealth military operation. Unfortunately, the radios needed for behind-the-scenes communication are often so bulky that stealthiness becomes a moot point. The huge antennas required to pick up radio waves transmitted over long distances essentially turn the vehicles carrying them into moving targets, and yet bigger antennas are needed if the military wants to cover more ground.

This week, engineers at the University of Wisconsin-Madison who took up the challenge trumpeted their success in solving the seemingly impossible problem of increasing the size of an antenna without making it physically bigger. To find a solution, they had to get creative.

“We are proposing to use the platform itself as the antenna,” said Nader Behdad, Ph.D., an associate professor of electrical and computer engineering at the university.

The team had been working on developing smaller, low-frequency antennas for electronic warfare since 2015, after receiving a $1.3 million grant from the U.S. Office of Naval Research. This time around, they focused on the high-frequency antennas needed to transmit signals over long distances and mountain ranges.

Military vehicles such as tanks are essentially huge metallic objects waiting to be turned into transmitter antennas.

The engineers were aware that the antennas they were working with were already as streamlined as they were going to get. But the vehicles the antennas were attached to presented room for experimentation. They realized that the trucks, armored cars, and assault vehicles that usually serve as platforms for antennas are, in essence, large metallic objects; and what is a military antenna, anyway, but a huge metal object?. Repurposing these vehicles allowed them to achieve what seemed impossible: augmenting the antenna’s reach without increasing its physical size.

Currently, the minimum height for an antenna picking up or transmitting high-frequency military signals is taller than the average adult. The physics of radio transmission dictates that antennas need to be roughly one-quarter of the length of the waves they are transmitting; military signaling uses waves that are, at the very least, 30 feet long. Strapping a 7.5-foot-long device to the side of a tank isn’t exactly inconspicuous. Transforming that tank into the device is.

The radiating sphere represents the theoretical strength of the radio signals emanating from the vehicle-turned-transmitter. 

“It’s a clever way to go around the limitations set by the laws of physics,” Behdad, told Phys.org. “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.”

The ability to turn existing vehicles into antennas will be a huge boon for military engineers looking to further streamline their vehicles for stealth purposes, and a much-needed one at that: Behdad’s new work thus far has been further encouraged by the U.S. Office of Naval Research, which recently gave him an additional $550,000 grant.

Not so sneaky.