Investigation and Development of a Lightweight, Efficient Low-RCS Multi-Function Antenna by Combining Conductive Composite Materials with Traditional Conductive Materials and Conductive Foams, 16-R8023

Principal Investigator
Patrick J. Siemsen

Inclusive Dates:  01/01/09 – Current

Background - Under previous internal research projects, SwRI investigated the use of conductive composites in making low-radar, cross-section (RCS) antennas. This research led directly to the development of the AS-142 MF/HF monopole direction finding (DF) antenna and the AS-420B VHF/UHF DF antenna. Both are in production for DF applications on a large number of surface combatants. Thanks to the success of these low-RCS receive-only antennas, significant interest has been expressed in using SwRI's conductive composite technology for high-power transmit antennas on current and future surface combatants, particularly to replace existing HF high-power transmit antennas, some of which are 35 feet in length. However, intolerable heating occurs when these conductive composites are used as high-power transmit antennas because of their lossy nature (inefficiencies). Also, the conductive composite material must be quite thick, which adds significant weight. For a 35-foot conductive composite monopole antenna with a wall thickness of 1.5 inches, the estimated weight approaches 1,000 pounds. Such weight is unacceptable for many applications.

Approach - The objective of this internal research effort is to develop a lighter weight, more efficient, low-RCS HF-band prototype antenna that can be used both for signal reception and for high-power transmission. To accomplish this objective, a novel conductive composite hybrid approach will be developed that incorporates traditional conductive materials to improve the efficiency while retaining reduced RCS. One or more layers of conductive composite will also be replaced with electrically equivalent lightweight conductive foam to reduce the overall weight of the antenna.

Accomplishments - Through the use of numerical modeling, an efficient conductive composite hybrid has been developed with the innermost conductive composite layers replaced with metal. Only minor adjustments to the outermost conductive composite (or foam) layers were necessary to maintain adequate RCS reduction. To replace one or more of the conductive composite layers with foam, a manufacturing process has been developed in which the foam layers are created by injecting a foam cream mixture into a vertically oriented annular space using a syringe with a mixing nozzle and letting the foam work its way up the space vertically from the point of injection during the foaming process. The mold is created by using two, thin-walled tubular components of different diameters. These components become a permanent part of the antenna structure. The end result is a well-controlled foam fill with an acceptable density.

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