Millimeter-Wave Multibeam Endfire Dual-Circularly Polarized Antenna Array for 5G Wireless Applications

A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband 4 x 4 SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications.