High Gain Circularly Polarized Substrate Integrated Coaxial Line Fed Antenna Array for RFID Band

In this paper, a high gain microstrip patch antenna array for radio frequency identification (RFID) applications is presented. A four-probes-fed microstrip square patch antenna fed by a series power divider is considered as the radiation element of the array. After that, a 2 × 2 antenna array is realized with a second level series power divider feed network implemented with substrate integrated coaxial line (SICL) technology. The series power dividers are used to implement a two levels sequential rotation feed network for generating circular polarization (CP). The SICL based feed network is found to effectively reduce coupling effects between feed network and radiating elements. Measurement results show a S
₁₁
≤ -15 dB bandwidth of 840 - 980 MHz, and gain of 11.8 dBi at the frequency 915 MHz. This antenna array is suitable for outdoor long-distance RFID communication systems.