N141-069 TITLE: Compact, Collapsible, or Conformal Antenna Design for Emerging High Power Radio Frequency (HPRF) Sources

TECHNOLOGY AREAS: Ground/Sea Vehicles, Battlespace, Weapons

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop a wideband, small aperture antenna exhibiting > 10 dB gain for emerging HPRF sources over the mid-VHF to low L band frequency range, with increased capabilities in operational reconfiguration, frequency tuning, bandwidth, and field of view.

DESCRIPTION: One of the main challenges for HPRF radiation is the integration of antennae in the propagation environment (ground and sea surface in various sea state conditions) into the system design configuration. Current wideband antenna concepts are largely focused on omni-directional radiators derived from simple dipole antenna designs, sometimes with corner reflectors and other simple modifications. However, all of these efforts provide only minimal gain, with the state-of-the-art currently only 2-3 dB across the desired bandwidth. Furthermore, emerging architectures are limited in power handling capability to tens of Watts or perhaps kW. The antenna is a critical sub-system that has not evolved to handle the diversity of HPRF waveforms and the MW power levels required in directed energy applications. Effective delivery of HPRF is made even more challenging with the complexities that arise with integration of antenna structures onto unmanned platforms, munitions, or other air delivered employment concepts. In typical antenna design, the physical size plays an important role in the gain and power handling capability, which leads to extreme challenges when requiring a compact, conformal, and lightweight design for proper system integration. Another key consideration is the intended operating environment of the system, of greatest interest for this effort is a naval environment. The antenna must be able to withstand large temperature fluctuations, maritime weathering (salt, wind, rain), and continuous UV exposure. Typical high power systems experience catastrophic degradation in this environment if not addressed with proper environmental mitigation techniques (i.e. radomes, UV protected dielectrics, etc.). Innovative improvements to the antenna architecture and/or materials are needed to achieve the higher gains necessary for increased range and could prove to be the critical factor in transitioning HPRF technology to the warfighter. A novel, compact, moderate-gain antenna design for MW+ powers is required with improved directionality to keep pace with the miniaturization of emerging HPRF technologies.

PHASE I: Perform a technology review of existing antenna technologies to determine the design feasibility and potential implementations of an antenna with moderate gain (10-15 dB) and compact size (less than 0.25 m^3), capable of operations at peak powers of 100 MW to 1 GW with repetitive pulse operation at 100s of Hz, and a characteristic impedance between 50 to 150 Ohms. Research efforts should also be made to determine the current limitations of antenna technology at the MW power levels for the volume specified and determine if any of the low power architecture technological solutions can be applied to achieve higher gain and/or powers. A down select of existing antenna technology should be conducted with a focus on determining what technologies provide the most useful capability for short pulse, MW class power operation while meeting the volumetric requirements. These antennae will be driven by an assortment of high voltage based RF sources, with pulse lengths shorter than 1 �s while utilizing damped sinusoid waveforms. This variation in sources leads to a requirement for a flexible, center frequency tunable antenna with a bandwidth of at least 20-30%, if not much broader. Efficient methods for numerical computation of electromagnetic and antenna radiation, new materials, devices and radiating systems for miniaturization and performance enhancement of the wideband antenna should be included in this analysis. Flexibility across bands, manufacturability, and real-time frequency reconfigurable antennas are stressed. The completion of Phase I will include the development of novel antenna designs to meet the outlined requirements using computational electromagnetic modeling and simulation, building on the antenna development for commercial applications at lower powers derived from the technology review efforts. The conceptual designs, along with the design implementation and antenna performance models should be included as well as a cost analysis and material development so as to ascertain critical needs not yet fully developed or readily available given current technology.

PHASE II: Phase II will involve the design refinement, procurement, integration, assembly, and testing of a proof of concept prototype leveraging the Phase I effort. The Phase II prototype will have a gain (10-15 dB), a compact size (less than 0.5 m^3), and be capable of greater than 50 MW to 500 MW output at a rep-rate of 10s of Hz, and a characteristic impedance between 50 to 150 Ohms. The prototype should also be capable of operating in an outdoor environment. This prototype must demonstrate a clear path forward to a full scale prototype based on the selected technology. Data packages on all critical components will be submitted throughout the prototype development cycle and test results will be provided for regular review of progress. The development of actual hardware and empirical data collection is expected for this analysis. A refined design package should also be submitted that meets the solicitation objectives with moderate gain (10-15 dB), compact size (less than 0.25 m^3), and operations at peak powers of 100 MW to 1 GW with repetitive pulse operation at 100s of Hz.

PHASE III: The performer will apply the knowledge gained during Phase I and II to build and demonstrate a full scale prototype device capable of 10-15 dB gain, compact size (less than 0.25 m^3), and operations at peak powers of 100 MW to 1 GW with repetitive pulse operation at 100s of Hz, and a characteristic impedance between 50 to 150 Ohms. Data packages on all critical components and subcomponents will be submitted throughout the development cycle and test results will be submitted for regular review of progress. The prototype will represent a complete solution and include all system elements including the RF connectors, RF feed, RF transition, and antenna. The prototype should be ruggedized for, at a minimum, testing in a shipboard environment across a temperature range of -20 �C to > 70 �C, MIL-STD shock and vibration, and be environmentally enclosed.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Potential commercial applications include a variety of communications, sensor and medical applications requiring compact, high power RF systems.

REFERENCES:
1. Balanis, Constantine A. "Antenna theory: Analysis and design, 2005." ISBN: 0-471-66782-X.

2. Milligan, T. A. "Modern antenna design, 2005." Hoboken: John Wiley & Sons.

3. Kraus, John D., and Ronald J. Marhefka. "Antenna for all applications." Upper Saddle River, NJ: McGraw Hill (2002).

4. Zhang, Qi, and S. T. Pai. "Introduction to High Power Pulse Technology." (1995).

5. Benford, James, John Allan Swegle, and Edl Schamiloglu. High power microwaves. Taylor & Francis Group, 2007.

6. Giri, D. V., et al. "Switched oscillators and their integration into helical antennas." Plasma Science, IEEE Transactions on 38.6 (2010): 1411-1426.

KEYWORDS: High power radio frequency; high power microwave; directed energy weapons; antenna

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