A zero-phase-shift line (ZPSL) grid loop antenna with enhanced magnetic field distribution

In this paper, a zero-phase-shift line (ZPSL) grid loop antenna is proposed to enhance the magnetic field distribution over a large interrogation zone for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. A new type of ZPSL structure is presented to achieve a small phase lag along the loop antenna. The measured results show that the proposed ZPSL grid loop antenna achieves impedance matching over a frequency range of 900-1000 MHz with a reflection coefficient smaller than -10 dB, and produces a uniform magnetic field distribution within a large interrogation zone of 200×200 mm².