High-Gain Windmill-Shaped Circularly Polarized Antenna Using the High-Order Mode and Ground-Edge Diffraction

In this letter, the high-order mode and ground-edge diffraction of a slot antenna are used to achieve a high gain. To inhibit the multilobes at the high-order mode, ground-edge diffraction is utilized to form a single main lobe by changing the size of the ground plane of the slot radiator. Then, this slot antenna is employed to construct a windmill-shaped array antenna for circular polarization. A four-way sequential-phase feeding network is designed to feed the four slot elements, which are placed in orthogonal positions to form a windmill shape. A reflector is placed under the four slot elements to make the proposed antenna unidirectional. The slot elements are excited in the high-order resonant mode, instead of the fundamental resonant mode, and ground-edge diffraction of the slot elements is used to make the radiation pattern form a single strong lobe with increased gain at the +z -direction. The antenna is studied and designed using simulation and measurement. Measured results show that the proposed antenna has a common bandwidth (overlapping of the impedance bandwidth, the axial-ratio bandwidth, and the 1 dB gain bandwidth) of 4.73-5.53 GHz (0.8 GHz, 15.6%), a realized peak gain of 13.4 dBi, and an efficiency higher than 89.2%.