Raytheon Co. has been awarded an $8 million contract to construct a radar antenna the length of a football field that has an extraordinarily precise and lightweight sensor and can be bonded to the hull of a floating, blimp-like airship. The contract is part of DARPA's Integrated Sensor is Structure (ISIS) program.An artist's concept of an unmanned airship 150 to 300 meters long that could hover for extended periods above the jet stream at altitudes of 65,000 to 70,000 feet. Raytheon is developing an active electronically scanned array antenna that would be bonded to the hull under an $8 million DARPA contract. (PRNewsFoto/Raytheon Co.) The active electronically scanned array (AESA) antenna would be bonded to the hull of an unmanned airship 150 to 300 meters (164 to 328 yards) in length that could hover for long periods above the jet stream at altitudes of 65,000 to 70,000 feet. The antenna would transmit on UHF and X-band. Raytheon Space and Airborne Systems (SAS) is providing the technology, which uses no moving parts to scan at nearly the speed of light. "DARPA wants to be able to look for airborne and ground-based targets and to communicate directly with the battlefield from a single antenna," said Michael Wechsberg, director of radio frequency systems programs for the Advanced Concepts and Technology Group of SAS. The low-power density radar would derive its extraordinary sensitivity from an extremely large aperture that would occupy much of the surface of the airship. "The mission is to develop an inordinately sensitive and lightweight sensor that can be integrated into the structure of an airship, which could remain essentially motionless over an area for a long time," Wechsberg said. "That would let us see targets moving very slowly from a platform that would be difficult to find, let alone to knock down." Developing the lightweight radar antenna technology is only part of the assignment. SAS will also have to find a way to bond the radar to the hull or other structure of the airship to save weight. "Using the hull as the support structure for the antenna eliminates thousands of pounds that would ordinarily be needed to provide and maintain a consistent shape for the array," Wechsberg said. "A much larger antenna, therefore, could be carried. The program envisions the largest X-band antenna ever built." Although it would contain millions of electronic components, the thickness of the antenna as envisioned by Raytheon would be about one centimeter (0.4 in). Only when bonded to the hull of the airship would the array be stiff enough to behave properly as an antenna. The main challenge for the bonding technology is a hostile environment. Bonding agents must be able to withstand ambient temperatures of -80 °C (-112 °F). The agents also must be able to accommodate differences in thermal properties between the antenna material and that of the hull. These properties would vary broadly. "So we need to come up with a way that in cyclical extremes of temperature will keep everything from coming apart," Wechsberg said. For more information, visit: www.raytheon.com