Development of a Conformal High-Frequency Antenna for 
Modern Naval Requirements, 16-9137

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Principal Investigators
Russell C. Rittimann
Ruell F. Solberg Jr.
John H. Hughes

Inclusive Dates: 04/01/99 - 01/15/01

Background - Traditional radio direction-finding (DF) antenna arrays are fabricated from materials that inherently have relatively large radar cross sections (RCS). These antennas are usually mounted near the mast tops or at other exterior locations on naval surface combatants. All these factors serve as a disadvantage when stealth is important. Recent naval ship designs have incorporated smooth and angled exterior surfaces to reduce their radar signature. For these advanced ships, a need exists for high-frequency (HF) DF antennas with minimum surface discontinuities that match or complement the contours of the ship or platform surfaces. SwRI has developed low-RCS DF antennas for very high frequency (VHF) and ultra high frequency (UHF) use, but they are not applicable for HF.

Approach - The objective of this program was to develop a new HF DF antenna for use on the next generation of stealth surface combatants with performance equivalent to the current antennas (AS-145). The design of the antenna optimizes sensitivity and DF performance while minimizing the radar cross section. A breadboard antenna was fabricated to allow measurements and tests to be performed to evaluate and to verify the antenna.

Accomplishments - The antenna design incorporates ferrite core orthogonal crossed-loops with a very low physical profile compared to existing HF antennas (inches compared to feet). The ferrite core loops were designed to operate from 0.5 to 30 megahertz at 100 watts continuous power input. This design minimizes the overall antenna size while maximizing the sensitivity. The design also allows the antenna to be mounted on bulkheads or recessed into the ship's hull so that the exterior of the antenna conforms to the hull or surface on which it is mounted. The antenna is inherently rugged to withstand the severe environmental and operational conditions of shipboard usage. Radar cross section has been minimized by shaping of surfaces and the addition of radar-absorbing material. The antenna, designated AS-141, is a candidate for installation aboard the U.S. Navy DD-21, LPD-17, DDG-51 and CG-47 class ships. Additionally, the AS-141 HF DF antenna is suitable for mounting on buildings and other less severe environments where low observability or obtrusiveness is necessary.

The AS-141 conformal high-frequency, direction-finding antenna

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