Superdirectivity and electrically small antennas

Abstract

Superdirective Antenna Arrays (SDAs) achieve exceptionally high end-fire directivity through reduced element spacing and precise excitation of the linear array elements. However, since their theoretical discovery over a century ago, SDAs have been dismissed due to the trade-offs arising from excessive directivity, specifically low efficiency, feed network complexity, narrow bandwidth, and sensitivity to manufacturing and environmental variations. More recently, influenced by advancements in materials science, computational modeling, and innovative design strategies, SDAs have experienced a renaissance. In this thesis, a series of design methodologies were developed and experimentally validated to overcome these historical limitations and enable efficient, compact, and practical SDAs. The work begins by demonstrating a high radiation-efficiency SDA design using amplitude- and phase-optimization, challenging the prevailing notion that superdirectivity necessitates significant loss. To further enhance practical viability, Super Realized Gain is introduced. Moreover, a novel approach in which the required reactive loading is embedded directly into the antenna geometry through careful dimensional tuning, thereby eliminating the need for discrete loading components. Following this, the introduction of a phase-only optimization strategy, which utilizes constant amplitude excitations, dramatically simplifies the feed architecture. These techniques, when applied to electrically small antenna (ESA) arrays, including designs based on meandered dipoles and parasitic reflector configurations, are validated. Full-wave simulations and experimental measurements confirm that these structures achieve realized gains exceeding conventional theoretical bounds. Overall, the thesis provides a comprehensive framework for the realization of practical SDAs, bridging the gap between theoretical potential and real-world implementation. The proposed designs are well-suited for emerging wireless communication and sensing platforms, particularly in scenarios that demand compact, highly directional antennas with minimal system complexity.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Department for the Economy
Supervisor	Stylianos Asimonis (Supervisor), Oleksandr Malyuskin (Supervisor) & Dmitry Zelenchuk (Supervisor)