James Tuss

Qualitative assessment of smart skins and avionic/structures integration

Current military aircraft employ multiple single function antennas installed at different locations to provide communications, navigation and identification (CNI), electronic warfare and radar and weapon delivery in the .15 to 18 GHz frequency bands. The smart skins concept, wherein several antennas are integrated into one (or a few) multifunction apertures conformal to the outer geometry of the aircraft, promises considerable benefits. These include extended antenna coverage, efficient use of aircraft realestate, quick installation and replacement and structural weight savings. However, to realize these payoffs, several disparate technical and operational issues such as development of multifunction apertures, integration of the radiating elements and repackaging the electronics into load-bearing structure, antenna isolation and resource management, and tolerance to low velocity impact damage, need to be resolved. Potential payoffs and the technical challenges of smart skins implementation and avionics repackaging is discussed in quantized transitional states from black box avionics traditional packaging to structurally integrated avionics of the future. Qualitative assessments of related smart skin technologies and risk reduction approaches, which could transition the technology to current and future aircraft, are proposed, and preliminary cost estimates presented.

Smart Skin Conformal Load-bearing Antenna and Other Smart Structures Developments

Developmental research efforts are underway investigating the use of innovative materials and design methodologies to enhance aircraft performance. This research discipline is commonly referred to as smart structures and materials. In general terms, smart structures utilize conventional and smart materials to sense their operating environments, analyze the resulting information, and actuate the structure in response to the sensed input. Research in the smart structures arena may be further divided into three distinct components: smart skins, vibration suppression, and adaptive structures. All components share the common purpose of enhancing vehicle performance and/or eliminating structural dynamics problems associated with current and future aircraft. Under the smart skins specialty, the primary technology discussed is the embedment of radio frequency antenna elements within conformal load bearing structures such as aircraft wing and fuselage skins to improve avionics and structural performance while reducing airframe maintenance costs, weight, signature, and drag. The role of conformal load bearing antennas as a key facilitator for smart skins is presented hi some detail with projections for near term technology applications. The other key smart structures initiatives are also covered to complete the picture.

Air vehicle integration issues and considerations for CLAS successful implementation

Over the last decade, Northrop Grumman Corporation under internal and DoD funding, and others, have been working on integration of RF antennas into load-bearing aircraft structures. This multidisciplinary effort, collectively referred to as Conformal Load-bearing Antenna Structures (CLAS), requires concurrent consideration of structural and antenna performance issues and has involved a team consisting of avionics, structures, material, and manufacturing expertise. From the published articles to date it could be argued that the technology has had some spectacular success in its initial stages but not much has been published about the issues raised by CLAS that would still need to be addressed and solved for final technology inclusion in an operational air-vehicle. Presented are some key results from the Air Force Research Laboratorys (AFRL) Smart Skins Structures Technology Demonstrator (S3TD) program that while funded from the Air Vehicles Directorate looked at the total picture of integration from a multidisciplilnary standpoint. Issues related to airframe integration are also discussed that need further study and evaluation before CLAS can be sanctioned as a viable future DoD technology. Such topics, in no particular order of priority are 1) airframe CLAS panel location, 2) airframe configuration issues, 3) EMI/lightning issues, and 4) repair issues and supportability, 5) panel design enhancement, risks, and issues.

A Broadband High-Gain Bi-Layer LPDA for UHF Conformal Load-Bearing Antenna Structures (CLASs) Applications

A broadband high-gain bi-layer log-periodic dipole array (LPDA) is introduced for conformal load bearing antenna structures (CLASs) applications. Under the proposed scheme, the two layers of the LPDA are printed on two separate thin dielectric substrates which are substantially separated from each other. A meander line geometry is adapted to achieve size reduction for the array. The fabricated and tested array easily exceeds more than an octave of gain, pattern, and VSWR bandwidth.

A MEMS reconfigurable pixel microstrip patch antenna for conformal load bearing antenna structures (CLAS) concept

A four by four pixelated microstrip patch antenna is reconfigured in three frequencies using RF MEMS switches. The proposed antenna can be integrated within a physical structure under the CLAS concept which can replace bolt-on antennas. Structural testing of the antenna clearly demonstrates the structural robustness of this CLAS reconfigurable antenna.

Aperture coupled MEMS reconfigurable pixel patch antenna for conformal load bearing antenna structures (CLAS)

The study and design of an aperture coupled MEMS reconfigurable pixel patch antenna is proposed for operation under the CLAS concept. By activating and deactivating certain sections of a pixelated area the antenna is reconfigured in three frequency bands within 1-2 GHz. Simulation results show that the antenna bandwidth ranges from 5% to 25% and the peak realized gain is greater than 9 dBi.

A pixelated pattern reconfigurable Yagi-Uda array for conformal loadbearing antenna structure (CLAS)

A conformal pixelated pattern reconfigurable Yagi-Uda array is proposed. The array operates at around 2.5 GHz and can steer the beam in the 45 and -45 degree directions with the help of RF switches and a metal reflector placed 1 inch below the array surface.

A broadband VHF-UHF Yagi-Uda end-fire array

A broadband VHF-UHF end-fire Yagi-Uda array is proposed for possible air vehicle integration and operation within the 240-465 MHz frequency band. The array consists of a driven dipole, a reflecting dipole, and three directing dipoles. The broadband impedance, pattern, and gain responses are obtained by adding two parasitic metal strips adjacent to a fat driven strip dipole. The array has a peak gain greater than 7 dBi and Forward to Backward ratio (F/B) greater than 13 dB throughout most of the operating frequency band.

Conformal direct written antenna on structural composites

The experimental studies of a conformal direct written antenna is presented. Investigation results of transmission lines fabricated using direct writing are presented followed by array results. It is shown that a direct written array on structural composite operates at around 2 GHz and can direct its beams in the 45 and -45 degree directions with the help of a metal reflector placed 1 inch below the array surface. The array provides a peak gain of 7 dBi.

Superstrate configurations for a MEMS reconfigurable pixelated patch antenna for CLAS

The experimental and simulation studies of an aperture coupled reconfigurable pixelated patch antenna for CLAS applications is presented. The antenna active dimensions are reconfigured to attain a wide swath of bandwidths within the 1-2 GHz frequency range. Simulated return loss bandwidths are between 8%-26% while measured bandwidths are between 6%-24% when the antenna is reconfigured from low to high frequency bands.