Next Big Thing in Army SATCOM: Tiny Antennas For Combat Vehicles
The idea is to do away with bulky satellite communication dishes and replace them with low-profile distributed aperture terminals — several small antennas working together to act as a single large antenna. The Army has been interested in this technology for years but only started a serious push in 2013.
The problem for the Army is that current SATCOM systems are too bulky and cumbersome to fit inside heavy vehicles like the Bradley or the Abrams tank that have turreted weapon systems. The turret has limited space and power available for a traditional mobile satellite terminal.
The Army’s communications technology lab has identified distributed aperture terminals as a technology that could help shrink SATCOM systems so that they can be installed in Bradleys and tanks. This is important for the Army because these are the vehicles that leaders use as their moving command posts when they go to war. A big dish antenna on top automatically turns them into high-value targets.
Because of the space and power limitations in turreted vehicles, SATCOM systems have been a huge headache for engineers trying to squeeze terminals, modems and power amplifiers into tanks or Bradleys.
The Army Communications Electronics Research & Development Engineering Center’s (CERDEC) space and terrestrial communications directorate at Aberdeen Proving Ground, Maryland, last year awarded Harris Corp. a 29-month, $10 million fixed-price contract to build a distributed aperture satellite communications system in a Bradley infantry personnel carrier. A functioning prototype is due in 2016.
“This is disruptive technology,” said Scott Potter, a program executive at Harris corporate headquarters in Melbourne, Florida. “We are combining energies from multiple apertures so electrically they look like one,” Potter told National Defense. “There’s nothing comparable.”
Distributed aperture architectures are found in big-ticket weapons systems like the F-35 joint strike fighter, but they have been considered too expensive for ground combat vehicles.
In a distributed aperture terminal, small antennas can be inserted on the sides of the turret or other areas on the exterior of the vehicle, whereas traditional terminals must be mounted on the top of the turret.
“It’s going to be a big challenge for us,” Potter said. “When you get live TV on commercial airplanes, those are probably from distributed apertures,” but the technological hurdles of building a distributed aperture terminal that receives and transmits signals from a moving vehicle on the ground are much greater, he said.
With a traditional satellite terminal in a turreted vehicle, the line of sight to the satellite can be blocked by the turret, which degrades service. SATCOM systems also can block the lines of sight and firing lines of the vehicle’s weapon systems.
With distributed small antennas, a network is less vulnerable to disruptions or blockage, he explained. “Some of the apertures have better visibility of satellites than others,” he added. “Maintaining that link is paramount. Distributed apertures should do well. If one is degrading the others can take up the slack. With a single aperture, if you lose it you lose the whole link.”
Harris engineers also will have to figure out how to install apertures with minimal damage to the vehicle’s armor. Compared to dish antennas, though, “smaller apertures will be less invasive, with smaller concentrations of power and wirings,” said Potter.
In a “request for information” published in June 2013, CERDEC pointed out that conventional terminals require a minimum of 400 to 900 square inches of continuous vehicle surface area for the antenna. Distributed aperture terminals may require a similar size area, but do not have to be continuous, and could be installed on the top and the sides of the vehicle. “Additional cable runs and vehicle penetration points may be needed for the distributed aperture solution. In the case of heavy vehicles, it will be very restricted, if not forbidden, to add additional breaches to the vehicle hull,” said the RFI. “A single entry point is likely required.”
The Army also worries that traditional SATCOM terminals put crews at risk of being exposed to harmful radiation. “The beam projects a hazardous radiation from concentrated microwave energy,” Potter said. “When the apertures are spread out all around the vehicle, they can direct the radiation away from the vehicle hatch.”
The Army also wants SATCOM systems that consume less electricity so they reduce the need for extra generators and auxiliary power systems. Harris was asked to make the distributed aperture terminal in the Bradley operate with only 750 watts. That is going to be tough to do, Potter said. A typical vehicle may have two to four kilowatts of electricity available, and 750 watts is “very little power for communications systems.”
The Army has set a cost target for the distributed aperture system of $150,000 per vehicle. That compares to about $250,000 to $300,000 per vehicle for current systems. CERDEC asked Harris to develop the terminals in an open standards architecture that is hardware agnostic. “The government wants to bring in other firms for open standard architecture development,” he said. “The key is that when technology refresh is needed, you don’t replace the entire terminal as technologies mature. … Plug and play is the name of the game. Many companies don’t like it.”
Military SATCOM expert Mike Barthlow, a former Marine Corps officer and now vice president of Cubic Corp., described the distributed aperture technology as “game changing.”
Notably, using small apertures makes vehicles less susceptible to detection by enemies. Multiple phased arrays distributed in a platform, and low-profile antennas are features that front-line commanders have wanted for years, Barthlow said in an interview. “That’s a very interesting technology.” Also, this system addresses the “size-weight-power” problem. “The phased array technology is a very attractive way to solve that. Every war fighter wants more capability in a smaller package with less power consumption.”
The challenge will be to get the desired data rate required for battle command, Barthlow said. “If you have a large SATCOM dish, it’s a more efficient technology to get the data rate through. If you put [in] a phased array, when you are doing electronically steered beams, it has different characteristics. They are going to have to continue to work that, and manipulate physics.”
If Harris can successfully deliver a working prototype, the Army might consider installing distributed aperture SATCOM terminals in other heavy vehicles. At least that is the goal of the program office that provides the Army’s current SATCOM system, the Warfighter Information Network-Tactical, or WIN-T.
According to the CERDEC solicitation, the WIN-T program has an “immediate need to integrate a satellite on-the-move terminal onto the heavy vehicles.” An industry source said neither the Bradley nor the Abrams has enough space to mount it, and engineers can’t make enough trades with the rest of the vehicle electronics to accommodate it.
WIN-T is a high-speed and high-capacity tactical communications network that the Army started acquiring more than a decade ago. A priority in recent years has been to make the system lighter, smaller and less complex, in response to poor customer reviews.
The newest version of WIN-T has been installed in Humvees, MRAP trucks and in Stryker light armored vehicles. But not on Bradleys or Abrams tanks.
Chris Marzilli, president of General Dynamics Mission Systems, the manufacturer of WIN-T, would not comment specifically on CERDEC’s initiative to produce a distributed aperture terminal. But he said that substituting current 20-inch dish antennas with distributed aperture terminals could be part of a broader effort to modernize WIN-T in the coming years. “SATCOM is getting more compact. The computing environment that supports signals inside the vehicle is getting smaller,” he told National Defense.
“All kinds of evolution is happening,” said Marzilli. “We are already working on next generation SATCOM on-themove terminals, with size, weight and power in mind. They are getting appreciably smaller.”
Integrating SATCOM systems into a heavy fighting vehicle with a turret is a daunting task, he said. “Every nook and cranny is precious. It has to be well thought through.”
WIN-T mobile SATCOM so far has not fared well in operational tests. Among the hiccups is the ability to provide connectivity to mobile units at the company level. The system has a “soldier network extension,” or SNE, which is an eight-foot wide trailer vehicle that includes a satellite transponder and computer for connection to the WIN-T network. It extends the network from the brigade down to the company level. The SNE had “major usability and reliability problems,” wrote the Defense Department’s top weapons tester J. Michael Gilmore, in his fiscal year 2014 annual report.
The SNE, which has a large dish antenna, is needed to help other vehicles in a unit secure a satellite signal so they can send and receive information. One problem with the SNE is that it requires significant setup time, so instead of providing communications “on the move,” it does communications “on the quick halt,” Potter said. The Army’s goal is to give commanders high-rate communications in moving vehicles with little to no setup delays.
In the long run, Potter and other experts pointed out, even if technologies like CERDEC’s distributed aperture terminal are successful, their future still depends on whether WIN-T can overcome its current troubles.