A Compact Circularly Polarized Array Enabled by a Slot-Coupled Feeding Network

This letter proposes a compact circularly polarized (CP) antenna array enabled by a slot-coupled feeding network. By introducing open-ended branches and gradually widened terminals in inverted-F radiating elements, miniaturization of the antenna is achieved. The proposed CP feeding network exploits the inherent 180° phase difference of the non-resonant slot and incorporates 90° phase-delay lines to realize sequential CP excitation. When the feeding network is integrated with the radiating elements, an additional resonance is introduced, expanding the impedance bandwidth of the array from 5.5% to 14.9%. In addition, a Z-shaped slot is employed to effectively extend the axial-ratio bandwidth compared with a conventional straight slot. Simulated and measured results demonstrate that the proposed antenna achieves 4.5% CP bandwidth (845-884 MHz). The size of the antenna is only 0.231 × 0.231 × 0.064 λ₀³. The proposed design avoids the use of lumped elements or high-permittivity materials, providing a practical solution for compact CP arrays.