Citation

Norman, Nur Syazani and Azahari, Badrul Amin and Ahmad, Nazihah and Zainuddin, Norsiha and Jizat, Noorlindawaty Md. and Yamada, Yoshihide (2026) Normal-Mode Helical Antenna with Tap-Fed Impedance Step-Up for Near-Metal UHF RFID Systems. In: 22nd IEEE International Colloquium on Signal Processing and Its Applications, CSPA 2026, 1 May 2026 - 2 May 2026, Kuala Lumpur, Malaysia.

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Abstract

Normal-mode helical antennas (NMHAs) are unique for UHF RFID applications due to their compact size and the distinctive advantage in its simultaneous electric and magnetic current radiation characteristics. In comparison with the conventional dipole antennas, whose performance degrades severely in the presence of metal due to electric-field suppression, NMHAs have a dominant magnetic near field that is less sensitive to conductive surfaces. However, electrically short NMHAs exhibit very low input resistance, which made practical impedance is challenging, particularly for the RFID applications which require conjugate chip matching. This paper presents a compact, center tap-fed NMHA designed to achieve a controlled impedance transformation using a direct tap-feed structure by only controlling the tap dimensions. Unlike lumped matching networks or geometric modification of the helical radiator, the tap-feed approach enables systematic adjustment of the antenna input impedance while preserving the intrinsic electromagnetic behavior of the NMHA. By appropriately selecting the tap position along the helical element, the antenna input impedance can be matched to a 50 Ω reference, allowing stable characterization and evaluation of near-metal performance. Full-wave simulation results demonstrate stable impedance behaviour and maintain magnetic near-field characteristics when the NMHA is placed near metal surfaces. The proposed tap-fed NMHA establishes a robust and scalable baseline for subsequent RFID near-metal studies, where the tap matching impedance can be adjusted to match with the RFID chip impedance in the future work.

Item Type:	Conference or Workshop Item (Paper)
Uncontrolled Keywords:	Normal-mode helical antenna
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK5101-6720 Telecommunication. Including telegraphy, telephone, radio, radar, television
Divisions:	Faculty of Artificial Intelligence & Engineering (FAIE)
Depositing User:	Ms Rosnani Abd Wahab
Date Deposited:	01 Jul 2026 06:29
Last Modified:	01 Jul 2026 06:29
URII:	http://shdl.mmu.edu.my/id/eprint/16178

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