Circularly polarized crossed dipole antennas for handheld RFID reader

A small and single-layer crossed dipole antenna with two metal strips loaded for phase delay has been proposed to obtain CP radiation. The proposed antenna uses two unequal length dipoles connected in parallel to a coaxial probe feed and requires no matching network. The required power and phase relationships are obtained by proper choice of the two dipole lengths. Additionally, the antenna operates at its half wavelength orthogonal modes for the UHF band, and the two resonant modes for circular polarization radiation are generated by the phase delayed metal strip loaded. The measured impedance bandwidth for 10 dB return loss is 5.3%, ranging from 907 to 957 MHz, and the 3-dB axial-ratio bandwidth is about 12 MHz or 1.3% around the center frequency at 925 MHz.