Broadband Circularly Polarized Antenna Array with Sequential Rotation Feeding and a Windmill-Shaped Defected Ground...

To address the demanding requirements for high gain, wide bandwidth, and stable circularly polarized (CP) radiation in wireless local area network (WLAN) applications, this paper proposes and implements a broadband circularly polarized array antenna primarily targeting the 2.4-2.484 GHz ISM band. The design employs a coplanar waveguide fed broadband CP monopole antenna as the radiating element. A sequential rotation technique is utilized to form a four-element array, and a windmill-shaped defected ground structure is introduced to further extend the bandwidth. The antenna is fabricated on a low-cost FR4 substrate with overall dimensions of 0.98λ₀ × 0.98λ₀ × 0.008λ₀ at 2.4 GHz. Simulation and measurement results show that the array antenna achieves a -10 dB impedance bandwidth of 1.22-2.78 GHz (87.1% relative bandwidth) and a 3-dB axial ratio bandwidth of 1.85-2.66 GHz (35.0% relative bandwidth), ensuring sufficient margin over the target WLAN band. At the center frequency of 2.45 GHz, the antenna exhibits left-hand circular polarization radiation, with a measured peak gain of 8.2 dBic and a cross-polarization discrimination better than 20 dB. To verify its performance advantages in practical systems, the designed antenna was integrated into a ZigBee wireless communication system for data transmission testing. Under controlled conditions, the system employing the proposed antenna achieves a packet loss rate of 3.0% ± 0.4% in a complex multipath environment, significantly outperforming a traditional linear-polarized whip antenna (19.0% ± 1.1%). The results demonstrate that the proposed antenna, featuring wide bandwidth, high gain, and strong anti-interference capability, is a robust solution for WLAN access points and internet of things gateways.