Cavity-Backed Circular-Polarized Compact Slot Antenna for Handheld UHF RFID Reader

By associating advantages of conventional antennas (such as the microstrip patch, inverted-F antenna, planar inverted-F antenna, and wire loop antennas) with Babinet's principle, a new compact circular-polarized antenna structure is proposed for the handheld RFID reader in Europe UHF band. Consisting of a meandered slot loop structure and an electric conductor as a reflector, the proposed antenna offers a significant gain of 4.5 dBic and a large HPBW of nearly 120
^°
while the dimensions are retained only a quarter-wavelength at 868 MHz (86 mm × 86 mm × 12 mm). Furthermore, the circular-polarized (CP) performance of the proposed antenna is remarkable: axial ratio (AR) of 0.4 dB, 3 dB-AR-beamwidth of about 120
^°
at the resonant frequency, and stability of CP performance when the antenna is located near a conducting body.