Conformal Near Omni-Directional Antenna Design for Unmanned Aerial Vehicles (UAV)
Technical Abstract
TST proposes R&D of a conformal, switched array antenna (CSAA); a steerable antenna capable of a nearly omni-directional field of regard (FoR) that exhibits modest gain over “omni”. Steering. This is achieved by RF switch-selecting of elements of the array which include dipole or monopole elements and delay lines. This gain increase enables the following improvements: reduction of UAV transmitter power requirements and the attendant heat loads, improved interference and jamming suppression and improved Low Probability of Intercept (LPI) performance. Also, reducing power and heat load lightens extends the mission duration. We anticipate realization of a gain figure of 10 or more dB higher than that specified in the solicitation. The CSAA has no active components requiring only switches, hybrids, delay lines and radiators. This enables use of corporate (rather than distributed) transmitters and receivers and obviates the expense of custom ASIC of a traditional phased array antenna. The proposed work will study and recommend radiator geometry, elements and arrays, switch devices, conductor and dielectric materials, coating materials and methods as well as attachment materials. We will develop a high fidelity simulation model of the baseline antenna system, and thereby demonstrate coverage patterns for main lobe and side lobe characteristics.
Anticipated Potential Benefits
The anticipated benefits for commercial applications include moderate gain tracking antennas that conform to automotive surfaces, and commercial aircraft, as well. The properties of low aerodynamic drag, steerability and low implementation costs are attractive for these applications. Not only will this result in improved communications performance (longer range links, more reliable connectivity and high capacity) the conformality will reduce drag and thus improve fuel economy. A phase 3 program is envisioned where the CSAA basic taxonomy is applied over a large range of military air and terrestrial platforms. In a “Network on the Move” (NOTM) concept, many elements of a regiment may be interconnected to form a robust network where any element serves as a switch and router. Physical connections are made or dropped as the network geometry changes. The CSAA may be truck mounted or even mounted as an integral part of a combatant’s helmet. The beams are steered via an embedded CPU and inertial platform (i.e., a laser ring gyroscope) to maintain pointing. Beam discovery and tracking are interesting challenges for a system design, but the robustness of such a network has a strong payoff. Where capacity increases are greatly enabled (by a factor of 100 or more over that needed for voice traffic), new on-board commercial services such as in-flight internet connections at DSL rates and above for many passengers may be supportable. The air platform antenna performance is the Key Enabling Technology for this win-win strategy to be developed. The remainders of the network elements, for the most part, have already been developed and exist in terrestrial internet switches, routers, standards and protocols. Early services such as email, document transfer, JPEG imagery and real-time high quality music may be enabled through visible internet radio gateways. As capacity grows connectivity at T-1 rates and above may be supportable. Since availability of cellular telephones over many continents is ubiquitous, it is easy to imagine its interconnection to commercial aviation. The cell phone user may then leave his phone in the ON state during flight and continue its use as though he/she were still at the airport or their office. The directional antenna for connection to cell towers is made practicable since an omni antenna can “see” too many cell towers simultaneously. Being able to select only a few towers within the antenna beam’s footprint enables reliable connections and suppresses interference from all of the other towers that may be visible with an omni antenna. In these ways, the high gain conformal antenna is a major enabling extension of the passenger cabin to the business traveler’s daily environment where computation, internet, email, voice communications and teleconferencing are enabled. The CSAA enables the air traveler’s IT. Commercialization must start with the technological feasibility determined through studies and laboratory measurement. The technical community must be informed as to the potential service extension. This awareness will engender the formation of standards committees so that an enlightened and focused set of protocols is established to then extend IP and cellular services to the air traveler. When this system is in use in the commercial community, the DoD will exploit the ensuing infrastructure for support of defense agendas. This model of DoD-backed technology investment that is embraced and implemented by the private sector and then used by DoD as part of our defense infrastructure has happened over the course of events in the US and on a global basis. The best examples of this circular process are GPS Navstar, IDCSP and related SATCOM systems, Internet itself and all of the secure intranets that handle Government traffic, etc. There may come a time when military communications with aircraft will use some commercial infrastructure for ubiquitous connectivity, and the conformal switched array antenna will be a key enabling technology.
Current tactical communications network connectivity among highly mobile forces deployed over the extended battlespace exhibits serious limitations on connectivity, capacity and security. The extensive deployment of SINCGARS and EPLRS radios in the field requires longer ranges and more highly reliable connections than are currently enabled by line-of-sight distances for which these radios are designed. The UAV communications relay platform is desired to greatly extend the range of these radios by providing “bent pipes” to extend the communications and position reporting mission ranges. The UAV platforms must enable connectivity by means of antennas and radio repeaters. Since the UAV must be situated so that it can serve its designated area of the battlespace it’s visibility in all necessary directions is a critical requirement of the antenna design. The realization of Omni-directionality is critical to the mission performance. We propose to study an antenna design that provides this connectivity and enables enhancement of the radio links through the use of directional antennas that can be steered in all necessary directions over the battlespace. In contrast to a traditional Omni antenna, our approach provides substantial robustness to the links (better SNRs, lower interference and jamming vulnerability and lower intercept probability) but at the expense of some additional system complexity. This performance/complexity trade-off is central to the proposed study.
Dan Glauber
http://www.articlesbase.com/communication-articles/conformal-near-omnidirectional-antenna-design-for-unmanned-aerial-vehicles-uav-718325.html
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