Metamaterial‐based, miniaturised circularly polarised antennas for RFID application

Abstract

Miniaturised circularly polarised (CP) antennas based on dispersion-engineered metamaterial transmission lines (TLs) are proposed and developed for RFID applications. It is first studied and developed based on the equivalent circuit and dispersion curves of composite right/left-handed TL (CRLH-TL), which is featured by a novel/low-cost double-layered 3D structure, including metallic screws, one ground layer and metal-insulator-metal (MIM) capacitor loaded on the top layer. CP radiation is achieved by two crossed CRLH-TLs with a microstrip-slot coupling excitation. One CP antenna and one polarisation reconfigurable antenna, which utilise CRLH-TLs are then implemented, respectively. Compared with the conventional right-handed (RH) TL-based antennas (positive resonance-based antennas), miniaturisation is achieved by pushing down the dispersion curve to a lower frequency using larger LH capacitance or/and inductance. Negative-order resonances could be successfully excited by cascading π-type unit-cells. It shows similar radiation characteristics and additional size reduction as the positive resonance-based antennas. This antenna shows an electrical size of 0.24 λ0 × 0.24 λ0 × 0.03 λ0, a −10 dB bandwidth of 4.8%, and a peak gain of 4.2 dBic. It demonstrates advantages in terms of flexible size reduction, low cost, easy manufacturing, and good radiation performance, which are very suitable for 902–928 MHz UHF band RFID application.