Zeroth-Order Serpentine Antenna With Omnidirectional Radiation Pattern for Anti-Metal Tag Antenna Design

A new double-layered serpentine antenna is proposed for designing an anti-metal tag with an omnidirectional radiation pattern on metallic surfaces using the concept of electric and magnetic loop currents. The zeroth-order resonance (ZOR) structure here is made up of two closely stacked serpentine lines for providing the strong capacitive reactance and parasitic elements that are required for supporting the zeroth-order resonance. Also, the geometrical parameters of the double-layered serpentine structure can control the capacitive reactance for tuning the tag resonant frequency effectively. Due to the successful excitation of the ZOR mode, our tag antenna can generate a reasonably good omnidirectional radiation pattern with a consistent read range of 7.9 m– 8.9 m (at EIRP of 4 W) on metal in all directions in the azimuth plane. It has a uniform spatial coverage ( $>$ 8 m) in the entire azimuth plane. Additionally, the antenna’s good impedance matching allows for an excellent power transmission of $\sim 99$ %. The tag resonant frequency is found to be very stable and not affected much by any changes in the backing object and the maximum measured read range is $\sim 9$ meters in $\theta \,\,{=}\,\,\pm $ 50 o at 915 MHz. It has a footprint of 50 mm $\times50$ mm ( $0.153\lambda \times 0.153\lambda$ ) with a low profile of 3.38 mm ( $0.010\lambda$ ). Furthermore, the antenna configuration is a simple folded structure around the foam substrate, without comprising any complex structures.