Compact on-metal UHF RFID tag antennas using embedded inductance and huygens’ meta-element techniques

This thesis presents the design, development, and experimental validation of two high-performance ultra-high-frequency (UHF) passive radio-frequency identification (RFID) tag antennas specifically engineered for reliable operation in metallic environments. In such environments, conventional RFID tags typically suffer from severe impedance detuning, degraded radiation efficiency, unstable resonance, and limited read range due to strong electromagnetic coupling with conductive surfaces. To address these challenges, two complementary antenna architectures are proposed to achieve enhanced frequency stability, controllable impedance characteristics, and improved radiation performance within compact form factors suitable for industrial deployment. The first contribution presents a compact folded stacked-patch UHF RFID tag antenna incorporating embedded inclined inductive slots for on-metal applications. The folded configuration effectively minimizes the physical footprint while extending the surface current path to achieve resonance across the 860–960 MHz UHF band. The inclined slots act as embedded inductive elements, providing precise reactance control and enabling direct conjugate matching to complex RFID microchip impedances without the need for external lumped components. A comprehensive electromagnetic analysis of the embedded inductive mechanism was conducted through full-wave simulations and surface current distribution investigations. Fabricated prototype measurements show excellent agreement with the simulated results, validating the accuracy of the design methodology and electromagnetic modelling. The proposed tag achieves a measured read range of 16 m at its 918 MHz resonant frequency under 4 W EIRP, thereby confirming the effectiveness of the embedded inclined inductive tuning mechanism in enhancing impedance matching and overall tag performance in metallic environments. The second contribution introduces a folding-free dipolar patch RFID tag antenna integrated with a Huygens’ Meta-Element (HME) for gain enhancement under metallic mounting conditions. The HME is strategically positioned above the dipolar radiator to promote constructive coupling between electric and magnetic dipole responses, thereby enhancing forward radiation. Surface current analysis confirms the excitation of antiparallel current loops, validating the presence of Huygens’ resonance behaviour. Experimental validation demonstrates improved realized gain, extended read range, and enhanced resistance to metallic detuning compared to conventional dipolar RFID tag configurations. A realized gain enhancement of approximately 3 dBi was achieved with the HME-integrated dipolar configuration compared to the standalone dipolar tag, along with a measured read range of 8.23 m. These results confirm the effectiveness and feasibility of HME integration for passive UHF RFID tag performance enhancement. Collectively, the proposed antenna designs establish a comprehensive and fabrication-friendly for compact, high-efficiency on-metal UHF RFID tag antennas. The integration of embedded inductive slot and Huygens’-based metasurface enhancement provides practical and scalable solutions for robust asset tracking in logistics, manufacturing, and industrial environments. The findings of this research contribute new theoretical and experimental insights into the electromagnetic mechanisms governing platform-tolerant RFID performance and advance the development of next-generation passive RFID systems with improved robustness, efficiency, and deployment flexibility.