The antenna are required in military for land-based, naval, and airborne communications, as well as communications intelligence (COM- INT) and electronic warfare (EW) systems including communications electronic support measures (CESM) and communications electronic countermeasures (CECM). The aperture size is constrained by the dimensions of the host platform (e.g. aircraft or naval ship).
Antenna requirements for military applications include low profile, high efficiency, wide frequency band, highly integrated and conformability to the host platform. The low profile and conformality stem from the desire to blend the antenna into its surroundings to avoid easy visible detection and identification. These applications often require novel antenna solutions.
Low-profile antennas (LPAs) are of particular importance within the UHF band, where they are used as communications antennas on military platforms. In such applications, they reduce platform visibility and decrease overall antenna weight, which becomes critically important in airborne platforms. These benefits are enhanced in light of the many military vehicles that contain a multitude of protruding antennas for multiple communication links at UHF frequencies.
Another important parameter in the antenna design is the choice of materials that meet structural, electronic, and electromagnetic requirements. Material issues are paramount in integration, packaging, interference, and performance parameters such as efficiency and bandwidth.
Low profile antennas
DARPA has awarded Kerby-Patel applied electromagnetics researcher the 2015 Young Faculty Award (YFA) for research into flatter low profile antennas that can be employed on both manned and unmanned aerial vehicles for navigation and communications.
“I’m working on a new way to design low-profile antennas backed by high impedance surfaces,” says Kerby-Patel. “High impedance surfaces are a promising new material for antennas, but right now there is a lot of trial and error in the design process. We’re trying to eliminate that trial and error.”
Her research involves three components: First, she will develop a model that simplifies the physics of the antenna into an equivalent circuit. Second, she’ll compare the behavior of the actual antenna to the model using electromagnetic simulation software and real-world experiments. Finally, she’ll use the new physical detail captured by the model to create novel methods for designing low-profile antennas.
The Best Radio Antenna Is One That’s a Tank, according to University of Wisconsin engineers
Troops in the field communicate using relatively low frequency radio signals like HF band. The upside is that they don’t require much power and can travel long distances. But to operate efficiently, antennas need to be at least one-quarter the length of the radio waves ( that can range from 10 to 100 yards at HF band) they transmit . University of Wisconsin–Madison engineers are seeking to effectively enlarge antenna size by using the vehicle itself as an antenna as part of a project supported by the Office of Naval Research (ONR).
“We’re basically looking at using the ‘antennas’ traditionally mounted on military vehicles as a means of exciting the platform itself,” says Nader Behdad, associate professor of electrical and computer engineering at UW–Madison. “If a large metallic structure is there, why not take advantage of it?”
The team aims to design “coupling structures” that, when strategically placed on a vehicle, allow it to transmit or receive signals at low frequencies. The structures act as electric or magnetic dipoles “exciting” the main structure—that is, making it resonate at frequencies comparable to its size and shape. They can “tune” the vehicle to work as an antenna across a range of frequencies.
“Think of an armored personnel carrier for example,” Behdad says. “The dimensions are generally about 10 meters long. Some natural resonate modes of the structure resonate very efficiently at HF frequencies with different [stimulative] current distributions and radiation patterns. With the scale model we used, we showed that this works.”
The team’s goal is to achieve a bandwidth of 25 KHz at 2 MHz and a larger range at 10 MHz. Such bandwidth could allow for data transmission rates up to 100 Kbps, sufficient for voice and text data if not video or images
Engineering professor brings antenna capabilities to military armor
Villanova University Electrical and Computer Engineering Professor Ahmad Hoorfar, recently announced the development and successful testing of armor panels in providing multi-channel communications and advanced active protection for vehicles, ships and buildings. He has been working on wideband low-profile antennas that provide electronic warfare, jamming and communication capabilities for fiberglass ballistic and blast-resistant armor panels.
According to the company’s news release, “The multi-function armor eliminates the need for multiple high-profile communications antenna structures on military vehicles and ships, making them less visible and identifiable in hostile situations. The armor-encased antennas also have jamming capability to block radio signals, such as those used to remotely trigger explosives, including improvised explosive devices (IEDs).”
“One of the problems that many military communications systems have is that they use low frequencies — anywhere from 2 MHz to below 1 GHz,” says Nader Behdad, an assistant professor of electrical and computer engineering at the University of Wisconsin-Madison. “As a result, very often you see huge antennas sticking off of their vehicles.”
Behdad thinks that those enormous antennas could be scrapped for low-profile, broadband antennas — thanks to a different approach to antenna design that replaces large dipole antennas with a more compact and conformal multi-mode radiator.
With traditional dipole antennas, the lower the operating frequency of an antenna, the larger it needs to be. Rather than fighting the laws of physics and trying to lower the operating frequency of a single antenna, Behdad’s concept involves tuning multiple parts of the same antenna structure to radiate at different frequencies, using synthetic “metamaterials” to shape their radiation patterns so that they won’t interfere with one another. Composed of metals, dielectrics and other materials, metamaterials react to electromagnetic waves differently, based on their index of refraction, making it possible to manipulate two competing radiation patterns and make them work in tandem within one antenna.
The research was supported by a federal Small Business Technology Transfers program sponsored by the Office of Naval Research.
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