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

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 operating in the 2.4 GHz ISM band. The design employs a coplanar waveguide (CPW)-fed broadband CP monopole antenna as the radiating element. A sequential rotation (SR) technique is utilized to form a four-element array. Furthermore,​ a windmill-shaped defected ground structure (DGS) is innovatively introduced to further extend the bandwidth. The antenna is fabricated on a low-cost FR4 substrate with overall dimensions of 126 mm × 126 mm × 1 mm. 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 (AR) bandwidth of 1.85–2.66 GHz (35.0% relative bandwidth), completely covering the target band. At the center frequency of 2.2 GHz, the antenna exhibits left-hand circular polarization (LHCP) radiation, with a measured peak gain of 8.2 dBi and a cross-polarization isolation better than 15 dB. To verify its performance advantages in practical systems, the designed antenna was integrated into a ZigBee wireless communication system for data transmission testing. The results indicate that, in a complex multipath environment, the system employing the proposed antenna achieves a significantly lower packet loss rate (approximately 3.0%) compared to using a traditional linear-polarized whip antenna (19.0%), effectively optimizing the wireless link quality. The designed antenna features wide bandwidth, high gain, and strong anti-interference capability, making it suitable for WLAN, Internet of Things (IoT), and other wireless communication systems.