Planar Circularly Polarized Circular Antenna with Clover Slot for RFID System

A novel circularly polarized (CP) circular antenna for UHF RFID system is proposed and experimentally studied. By embedding a four-leaf clover slot into the circular patch fed by the L-shaped microstrip line, the proposed CP design can easily be achieved with the impedance bandwidth (RL >= 10 dB) of about 99 MHz (11.0% @ 925 MHz) and the 3 dB axial-ratio (AR) bandwidth of about 60 MHz ( 7 % @ 925 MHz) for UHF RFID applications. The measured peak gain and radiation efficiency are about 6.2 dBic and 90% across the operating band, respectively, with unidirectional pattern in the XZ- and YZ-plane.