Compact Single-Feed Dual-Mode Antenna for Active RFID Tag Application

This communication proposes a compact single-feed dual-mode antenna for active radio-frequency identification (RFID) tag application. The proposed antenna consists of a slotted patch on an FR4 substrate, a feeding microstrip line, and a foam spacer with a volume of only 60 mm × 50.3 mm × 6 mm (0.48λ₀ × 0.40λ₀ × 0.048λ₀, where λ₀ is the wavelength at the center frequency). It operates as a dipole in free space and as a patch when placed on a metallic surface. A prototype that can provide an impedance bandwidth of 390 MHz (2.28-2.67 GHz) in free space and 470 MHz (2.32-2.79 GHz) on a metallic surface is built and measured. The measured radiation patterns, peak gains, and radiation efficiencies in these two scenarios are provided.