Low-Profile Wideband Circularly Polarized Array Antennas Using Integrated Half-Power Quadrature Power Divider

Low-profile wideband circularly polarized (CP) array antennas using integrated half-power quadrature power divider (HP-QPD) are presented. A novel HP-QPD is first proposed as an important design concept for CP radiation. Detailed analyses show that the proposed HP-QPD can have half-power CP radiation and the remaining half-power transmission with equal-magnitude but quadrature phase difference. Therefore, it can be utilized for designing a 1 \times 2 CP array antenna. Compared to the traditionally designed single-feed or dual-feed CP counterparts, this 1 \times 2 array antenna can have more than four times wider axial ratio (AR) bandwidth with three CP modes and a simple feed network. This 1 \times 2 array antenna was then designed, fabricated, and measured for performance verification. Both measured and simulated results show that this array antenna can have a wide overlapped impedance and AR bandwidth of 7.9% with a thin dielectric thickness of 0.031\lambda {0}. The 1 \times 2 array antenna was further extended to a 1 \times 8 linear array antenna for high gain CP radiation. Measured results show that unidirectional and symmetrical radiation patterns are achieved with high peak realized gain of 15.4 dBic, low profile, and simple feed network.