N112-113 TITLE: Low Profile, Very Wide Bandwidth Aircraft Communications Antennas Using Advanced Ground-Plane Techniques

TECHNOLOGY AREAS: Air Platform, Sensors

ACQUISITION PROGRAM: PMA 290; Maritime Patrol & Reconnaissance Aircraft

OBJECTIVE: Develop controlled-impedance ground planes with reduced weight and thickness, and apply them to low-profile aircraft communications antennas.

DESCRIPTION: Current and prior efforts have addressed all aspects of reducing the size of an aircraft communications antenna operating in the Very High Frequency (VHF) and Ultra High Frequency (UHF) bands, but while good progress has been made, maintenance of reasonable gain at very low profiles and small diameters, especially as operating frequency is lowered, remains a problem. These two performance measures (gain vs. profile/diameter) are inversely related, so an improvement in one generally means a loss in the other. Further reductions may be achievable in the amount of surface area required on a given aircraft, but only at the expense of gain. Overcoming these limits necessarily involves bringing another variable into play, and the only variable left to exploit is the ground plane itself. It is conceivable that the ground plane could be treated with some engineered material that would overcome these limitations. Recent advances in materials sciences have yielded several ideas that could be exploited to achieve these goals.

The need for low profile is related to the need for minimal aerodynamic drag, and it is generally accepted that the maximum height above the aircraft surface should be no more than one inch, less if practical. An antenna that is flush with the surface is most desirable, but is not required for this topic. These antennas require a 360-degree field of view in the azimuth plane and operate over a frequency range of 30 MHz to a minimum of 600 MHz, and gain performance at the horizon must be improved while reducing thickness and diameter below currently practical levels. Important specifications are vertical polarization in the horizontal plane, a lower frequency limit of 30 MHz or lower, an upper frequency limit of 600 MHz or higher, the ability to handle 100 Watts of input power at 100 percent duty cycle from a combination of several radio sets operated simultaneously, and a nominal voltage standing wave ratio (VSWR) of 1.5:1 or less (2:1 maximum). Weight and surface area consumed are always important considerations and should be minimized. It is assumed that several radios will share the single input port, but isolation between them should be handled by separate circuitry. Minimal hull penetration is allowed, but the proposed antenna should not require modification of the existing aircraft skin beyond penetrations for fasteners and the antenna feed port. It is envisioned that current and future aircraft ranging from helicopters to large transport category aircraft, and from low-speed craft to supersonic craft will utilize this technology and each platform on which it is to be employed will require specific adaptations.

PHASE I: Develop and determine the feasibility of advanced ground planes for antennas and select one or more candidate approaches likely to be able to satisfy the requirements. Conduct computational analyses showing the limits of performance for the selected approaches. Select the best approach and demonstrate by practical or computational modeling that the approach has the potential to meet performance requirements.

PHASE II: Refine the design selected in Phase I and fabricate a technology demonstration model. Show the performance of this model through laboratory measurements.

PHASE III: Develop an engineering model antenna for a specific Navy platform, and demonstrate performance with actual antenna pattern measurements on a ground plane that fairly represents the actual aircraft mounting location.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial aircraft experience many of the same difficulties as military aircraft. The developed technology would be very useful on commercial aircraft.

REFERENCES:
1. Kabiri, A., Yousefi, L. & Ramahi, O. M. (2010). On the Fundamental Limitations of Artificial Magnetic Materials, IEEE Transactions on Antennas and Propagation.
DOI: 10.1109/TAP.2010.2048845

2. Volakis, J.L., Chen, C.C. & Fujimoto, K. (2010). Small Antennas: Miniaturization Techniques & Applications, McGraw-Hill, 2010.

3. Brewitt-Taylor, C.R. (2007). Limitation On the Bandwidth of Artificial Perfect Magnetic Conductor Surfaces. Microwaves, Antennas & Propagation, Institute of Engineering and Technology (IET), 1(1),255-260. DOI: 10.1049/iet-map:20050309

4. Werner, D.H. & Werner, P.L. (2003, June). The Design Optimization of Miniature Low Profile Antennas Placed In Close Proximity to High-Impedance Surfaces. Antennas and Propagation Society International Symposium. Vol 1, pp 157-160. DOI: 10.1109/APS.2003.1217424

5. Yeo, J. & Mittra, R. (2001, July). Bandwidth Enhancement of Multiband Antennas Using Frequency Selective Surfaces for Ground Planes. Antennas and Propagation Society International Symposium, Vol 4, pp 366-369. DOI: 10.1109/APS.2001.959474

6. Orton, R.S. & Seddon, N.J. (2003, March) PMC As An Antenna Structural Component, Twelfth International Conference on Antennas and Propagation 2003 (ICAP 2003), Vol 2 pp 599-602. http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01353715

KEYWORDS: antennas; wide-bandwidth antennas; low profile antennas; conformal antennas; controlled impedance ground-planes; affordability

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