Minaturized Sequentially Rotated Curved PIFA Circular Array for Portable Handheld RFID Readers

This paper describes the miniaturization process of a sequentially rotated circular array antenna implemented with three curved planar inverted-F antenna (PIFA) elements. The antenna miniaturization obtained by bending curved PIFA elements (resulting in closer antennas) makes the impedance matching more complex and, for this reason, a capacitive coupling mechanism is implemented to reduce the antenna impedance. An antenna with diameter 0.16? (calculated at 915 MHz) and height 0.05? has been numerically optimized to work within the radio frequency identification (RFID) ultra-high frequency (UHF) bandwidth, showing a joint S11?-10 dB, axial ratio (AR) ?3 dB, and right hand circular polarization (RHCP) gain?2 dBic bandwidth of 908-927 MHz.