Low-frequency antennas could be excellent combat and defense tools, if only they were small enough to fit onto ships and drones. They can be used in electronic warfare to jam radars and cut off an enemy’s communication or to jam the signals that remotely detonate improvised explosive devices. On the flipside, low-frequency antennas can also be used to listen to and track down enemies or the source of a hostile signal. However, there’s a catch: the longer the wavelength, the bigger an antenna must be, at least according to physics. Nader Behdad, an electrical engineer at the University of Wisconsin-Madison, has received a $1.3 million grant from the Office of Naval Research to design powerful antennas that push the laws of physics to their limits.
Low-frequency radio waves have great potential—this 3 to 300 MHz range has low signal attenuation, which is great for long-distance communication systems. Their long wavelength makes them excellent at getting around natural obstacles, such as mountains. However, the same characteristic makes this part of the spectrum especially challenging for military applications where there is no room for bulky antennas.
Behdad is designing a 1-meter antenna for jamming that can send high-power signals, even at the bottom of the low-frequency range. He plans to use a combination of vacuum electronics, which can handle high-power transmissions, and the concept of non-Foster impedance matching, a technique that uses negative inductors and capacitors to overcome some of the limitations of conventional circuits.
The researchers are also working on creating antennas that the Navy can use in the field to find the source of jamming. The technology for these new antennas will build upon Behdad’s previous work on electrically small antennas, which has resulted in several patents and dozens of published papers. The design will be inspired by the Ormia ochracea, a parasitic fly with such excellent directional hearing that electrical engineers have studied their ears to design microphones, hearing aids, and in Behdad’s case—biomimetic antennas. Now he is challenged with shrinking the technology to make it work for long wavelengths. If he succeeds, military personnel can use powerful antennas in more situations without being limited by their size.
