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Dispersion engineered electrically small antennas


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics OBJECTIVE: Design, fabricate, and demonstrate electrically small antennas with enhanced bandwidth going beyond the fundamental bounds dictated by Chu’s limit. The proposed electrically small antennas should involve dispersion engineered matching loads using tailored dispersive materials or circuits that will allow tailoring the bandwidth independently from the stored energy in the system, resulting in electromagnetic radiation with higher data rates than conventional antennas. Dispersion engineering may be achieved through suitable electromagnetic design, metamaterial loading, and/or circuit loads implementing desirable frequency dispersion features. The final layout should include all relevant components to tune the antenna for operation beyond Chu’s limit. DESCRIPTION: The need for broader bandwidth in electrically small antennas is one of the most challenging tasks in the general area of antenna design for energy and information transfer, and it is of particular relevance to DoD in the low-frequency regime. Significant advances have been recently made in the realization of electrically small antennas operating close to Chu’s lower bound on bandwidth, and theoretical proposals to overcome this bound have been put forward, with important opportunities for communication systems and energy harvesting. Chu’s lower bound on the quality factor of linear, passive, time-invariant, one-port dipole antennas characterized by a single resonance dictates the maximum achievable bandwidth for given volume and efficiency. Recently it has been recognized that simple matching networks with dispersive materials can overcome these constraints and operate beyond Chu’s lower bound. Dispersion engineering in the form of metamaterial loading, multiple coupled self-resonant modes and/or circuit loading relying on tailored loss and dispersion can be used to enhance the bandwidth of electrically small antennas beyond Chu’s lower bound, still retaining a passive approach. Antennas can be loaded with passive matching networks, which so far have been used to extend the bandwidth by coupling multiple resonances together in order to operate close to the Bode-Fano bound on matching bandwidth. This approach, however, comes with several drawbacks, including introduced signal distortion within the impedance bandwidth, large and dispersive group delay, and inefficiencies associated with a large stored energy. The goal of this STTR is to demonstrate passive electrically small antennas targeting the HF or UHF band supporting data rates beyond state-of-the-art antennas that approachChu’s lower bound. The antennas should have a return loss of at least -6dB at the input port, with a radiation efficiency larger than 70%, an effective stored energy equal or lower than that based on operation with a single-resonant matching network, and a flat group delay across the enhanced bandwidth of operation. The demonstrated antenna should be low-profile, with or without a closely spaced ground plane. PHASE I: In the Phase I effort, a complete design of a passive electrically small antenna operated beyond Chu’s lower bound shall be demonstrated. Proof-of-principle simulations based on accepted methods and computational techniques shall be provided. Comparison of performance metrics to include the bandwidth anticipated by the proposer, efficiency, group delay, and stored energy with conventional approaches to impedance matching of small antennas, should be carried out. PHASE II: In the Phase II effort, the experimental procedures outlined and begun in Phase I shall be realized, and the fabrication and full characterization of the radiation properties of the devices shall be reported. The radiation pattern as a function of frequency across the bandwidth proposed in Phase I shall be verified, clearly demonstrating the behavior proposed in Phase I. Demonstration of broadband response well beyond Chu’s lower bound should be sought after. Comparison of performance metrics to include bandwidth, efficiency, group delay, and stored energy with conventional approaches to impedance matching of small antennas, should be carried out in the experiments, and a demonstration of higher data rates in a standard communication setup should be pursued. PHASE III DUAL USE APPLICATIONS: The Phase III work will demonstrate the reliability and scalability of the proposed antennas, their compact form factor including the matching network and feed, and their integrability in standard communication systems, including applying relevant modulation strategies for signal communications. A partnership with industry to commercialize the technology will be created, aiming for both DoD as well as scientific and civilian applications. REFERENCES: 1. L. J. Chu, “Physical limitations of omni-directional antennas”, J. Appl. Phys. 19, pp. 1163-1175, 1948; 2. Yaghjian, Arthur D. "Overcoming the Chu lower bound on antenna Q with highly dispersive lossy material." IET Microwaves, Antennas & Propagation 12.4 (2018): 459-466; 3. Yaghjian, Arthur D., and Steven R. Best. "Impedance, bandwidth, and Q of antennas." IEEE Transactions on Antennas and Propagation 53.4 (2005): 1298-1324; 4. A. Mekawy, H. Li, Y. Ra’di, and A. Alù, "Parametric Enhancement of Radiation from Electrically Small Antennas," Physical Review Applied, vol. 15, no. 5, p. 054063, 05/27/ 2021 KEYWORDS: electrically small antennas; Chu’s limit; dispersion engineered
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