U.S. Air Force researchers use 3-D printers and other cutting-edge concepts to create the next innovations.
There is no Moore’s Law for antennas because size reduction and performance improvement will always be subject to the limitations imposed by electromagnetic physics and material properties. But steady advances in computer technologies, such as electromagnetic modeling and simulation and 3-D printing, enable antenna technology researchers to push the limits of possibility on behalf of the warfighters.
Scientists and engineers at the U.S. Air Force Research Laboratory (AFRL), Antenna Technology Branch, Wright-Patterson Air Force Base, Ohio, are taking advantage of these technological advances to develop next-generation antennas. Experts say metamaterials show great promise for military antennas, but the technology is not yet at a point where it is being manufactured widely. To help overcome that challenge, Air Force researchers use a 3-D printer to prototype antenna metamaterials that potentially could advance technology beyond the more conventional microstrip antenna. Small, lightweight, low-cost microstrip antennas, which were invented about four decades ago, are used in military aircraft, missiles, rockets and satellite communications as well as in the commercial sector.
“It allows us a capability in rapid prototyping that we didn’t have before,” says David Curtis, the AFRL’s Antenna Technology Branch chief. “It’s yielding some interesting things. It’s creating new ground planes for antenna elements.”
Using the 3-D printer, researchers are able to build a prototypical metamaterial for antennas. “The metamaterials composite is something we would really like to see because that could very well be a major breakthrough. A composite metamaterial could be engineered almost pixel by pixel, or atom by atom, to achieve some specialized function that modifies the wave as it propagates through the medium or the device,” Curtis explains. “Even though metamaterials as a composite are pretty far off into the future, hopefully it will be realized.”
Printing in three dimensions allows researchers to build the antenna metamaterial layer by layer, tailoring its capabilities as they do so. This may result in the fabrication of a doubly curved antenna that would not be fabricated easily using traditional microstrip. “This is a way to improve antenna performance and to be able to, in fact, manufacture prototypes of things we never could before. Microstrip or other types of media come in a printed circuit format that is more planar and rigid. With a 3-D printer, we’re able to gradually build up layer by layer an arbitrarily curved surface and then use metallization techniques after the fact to actually put circuitry onto the curved dielectric shape,” Curtis explains.
He adds that in one case, researchers achieved a four-to-one reduction in size and weight for an antenna over a state-of-the-art counterpart it was designed to replace. To do so, they used the 3-D printer to add a magnetic layer and then redesigned the antenna based on the inclusion of that layer.
AFRL researchers also are taking advantage of commercial electromagnetic modeling and simulation software, which enables new antenna element design and optimization that improve performance. Breakthroughs may help warfighters communicate in the increasingly crowded electromagnetic spectrum. “There is considerably more pressure these days to get access for commercial use to the spectrum that has previously been reserved for military use, so we’re seeing across the Defense Department an interest in being able to play nice in that contested environment where there’s so much demand for bandwidth,” Curtis says. “Wideband digital phased arrays composed of low-cost, frequency-agile electronics with distributed back-end data processing will be better suited to take advantage of diversity schemes and operate in congested spectrum environments.”
The AFRL uses both an indoor and outdoor range to help develop and test new antenna technologies. The indoor facility is known as a multifunction compact range anechoic chamber. It is designed to measure antenna radiation patterns, bistatic near-field scanning, radio frequency tomography and free space radio frequency experiments from ultrahigh frequency up to 40 gigahertz. The Air Force plans to upgrade the range so that it can handle up to 50 gigahertz. The indoor range complements the AFRL Sensors Directorate’s outdoor range, which allows the laboratory’s personnel to experiment with and test radar subsystem hardware and novel radar algorithms and techniques.
Among many and varied projects, Antenna Technology Branch researchers are developing open system architectures in an effort to establish an Air Force standard with industry, which will allow new functionality to be added in a plug-and-play manner, lowering costs. “Life-cycle cost is always a critical issue in any military system. For us, being able to have an industry standard for a modular system architecture will help realize long-term savings as well as flexibility and performance of complicated antenna systems,” Curtis declares. Projects include research and development of antennas for unmanned air vehicles and continued research into smart skins for aircraft, a capability first conceived in the 1980s.
The Antenna Technology Branch has a long history of technological breakthroughs, including in recent years a manpack portable suite. The 20-gigahertz portable phased array weighs 20 pounds and can be carried in a rucksack. “You open up the rucksack that a soldier carries, pop out the legs, press one button and within three minutes it will acquire a satellite and downlink wideband data. The purpose of this is for situational awareness of what types of threats might be over the hill or around the corner in a city,” Curtis reports. “The way this was demonstrated was to put it in a parking lot, and as the generals were looking at it, they pushed a button and got CNN.” Curtis declines to reveal whether the system has been fielded.
The Geodesic Dome Phased Array Antenna is considered another major breakthrough that came about because an Air Force customer complained that 10-meter-diameter dishes are too costly and asked for something that scans a beam in the same manner as a phased-array antenna. “[The AFRL] developed this faceted three-dimensional thing that looks like a soccer ball with pentagons and hexagons, and each facet is a planar phased-array antenna,” Curtis reports.
Other historic breakthroughs by AFRL researchers include developments in limited scan array antennas, monolithic microwave integrated circuits and phased-array technology for aircraft-to-satellite communications. Advances also include leading-edge research on metamaterials, including negative index materials and microwave printed circuits, also known as stripline circuits. Some of the technologies have transitioned to the commercial sector, including the stripline circuit; various amplifiers; and the Rotman lens, which is a time-delay, beam-steering technology used to eliminate beam-steering errors from scanned array antennas.
The branch focuses primarily on computational and fundamental electromagnetics, novel and applied antenna element design, phased-array architectures and control, and engineered electromagnetic metamaterials. The efforts are oriented toward applications in communications, radar, and intelligence, surveillance and reconnaissance. The organization strives to achieve higher system performance at lower cost and is addressing wideband and multiband concepts to share spectrum effectively.
The antennas branch has existed in various incarnations since 1947 when the Air Force Cambridge Research Center was created. It has endured three major reorganizations and is now part of the AFRL Sensors Directorate. It currently employs about 15 people and is rebuilding following a move to Wright-Patterson Air Force Base.