Northrop Grumman's Electronic Systems and Shipbuilding companies have started design work sponsored by the Office of Naval Research to demonstrate innovative approaches to the integration of radar antenna apertures with the deckhouse structures of future Navy surface ships.
Dr. Steve Russell, program officer for Topside Signatures in ONR's Sea Warfare and Weapons Department, says that the program, designated "aperstructures" (short for aperture-structures), "represents a new paradigm for the design and integration of antennas into topside structures."
The work, he says, will demonstrate an approach that achieves more effective integration of the two, as well as cost and weight savings and improved antenna performance. It also will evaluate solutions to other technology challenges related to the new approach.
Russell points out that antenna arrays for the Navy's new Zumwalt-class (DDG-1000) destroyer are installed within the ship's deckhouse to minimize the ship's radar cross-section. Because of the number of antennas it must accommodate, the ship's deckhouse, which is fabricated from composite material, needs to be reinforced, requiring the antennas to be installed within heavy steel stiffeners in so-called "picture-frame" mounts. As a result, the antennas, especially the larger ones, along with their steel support frames, add substantial weight to the deckhouse.
The aperstructures effort, Russell says, will demonstrate the feasibility of a less invasive approach to aperture-structure integration. The concept is to mount the antenna aperture in a recessed surface of the structure, eliminating the need to cut a hole in the deckhouse. The back-end antenna electronic components, including beamforming, transmit and receive, and power elements, are housed in a composite structure inside the deckhouse and linked to the aperture by RF cabling.
The design, Russell says, maintains the structural continuity of the deckhouse and preserves its design integrity and strength. Because the antenna uses the deckhouse structure for its support, it does not require a heavy steel mount, thereby achieving significant weight savings and freeing real estate for larger antenna arrays, allowing enhanced antenna performance.
ONR awarded approximately $9 million to Electronic Systems last summer and $9 million to Shipbuilding in September for the aperstructures program, which is expected to be complete in August 2011. Northrop Grumman Ship Systems will build a structural test article at its Gulfport, Mississippi, facility to serve as an integration platform. Northrop Grumman Shipbuilding is also conducting analyses of the composite joints that would be used in the array-structure merger.
The companies will integrate four antenna concepts including the Northrop Grumman S-band missile defense radar, a low-observable navigation radar designed by Georgia Tech Research Institute, a UHF line-of-sight radar built by Toyon Inc., and an X-band communications antenna from Ball Aerospace.
Russell says that, in addition to integrating the antenna array structure with the composite material of the ship's deckhouse, a key challenge is compensating for deckhouse motions that result from hydrodynamic forces on the ship. Because the array is integrated with the composite deckhouse, these forces may distort an antenna's surface and affect its ability to maintain a radar beam. The industry team is evaluating a concept called "dynamic metrology" that will enable the array to recalibrate itself on the fly. Another critical challenge, he says, is radar cross-section control to minimize the radar's effect on ship signature.
The Northrop Grumman aperstructure concept is targeted at CG(X), the Navy's next-generation cruiser, now in concept development, that will replace the Ticonderoga-class Aegis guided-missile cruisers. In parallel with the aperstructures effort, ONR also is pursuing an Integrated Topside Innovative Naval Prototype program that is looking at aperture integration on board submarines and other potential surface platforms.