Inversely-designed dispersion-engineered electrically small antennas

This proposal aims to develop electrically small antennas (ESAs) with broad bandwidth and high efficiency by minimizing the frequency dispersion of the antenna through dispersion engineering and topology optimization. Taking advantage of the anomalous dispersion that is present around the resonance of any resonant circuit with loss, we present a transformation that converts the dispersive impedance of an ESA to one with an anomalous dispersion, which can be easily canceled through a passive network with conventional dispersion, resulting in an overall impedance with a minimal reactive part. This allows us to increase the bandwidth of the antenna by orders of magnitude compared to the Chu limit and get very close to ultimate limit dictated by the Bode-Fano bound. Importantly, to achieve this goal, we do not introduce loss in the system, which can degrade the efficiency of the antenna, but we use the intrinsic real part of the antenna impedance. The approach proposed in this project is very general and can be applied to any type of ESAs. The concept was validated in Phase I using planar meander dipole ESAs with second-order dispersion-engineered passive matching networks incorporated in the antenna topology. The antennas operated at 200 MHz with ka ~ 0.4. The numerical and experimental results have demonstrated the possibility of implementing second-order  PNMs into the antenna geometry, leading to a 25% improvement in the antenna bandwidth compared to the control antenna without matching. Work performed in Phase II will optimize the matching network design, topology, and extend the concept to three-dimensional spiral antennas with the goal of developing prototypes that exceed the Chu limit.