A broadband slot antenna with unidirectional circularly polarized radiation patterns

A novel circular slot antenna is proposed in this letter to generate a broadband circular polarization (CP) wave. This antenna consists of a Γ-shaped radiator and a circular ground with a cut of three ellipses. By adjusting the size and position of these ellipses, a CP wave can be realized. A chip resistor, which is used to receive the currents and decrease reflection, can significantly enhance the CP bandwidth. The study of the effect to antenna performance of different geometric parameters has been conducted. The results show that good performance of impedance bandwidth (S₁₁ < -10 dB) is approximately 106.1% (1.01 ∼ 3.29 GHz), and 3-dB axial-ratio bandwidth is approximately 89.7% (1.26 ∼ 3.31 GHz). Moreover, the antenna exhibits a stable average gain of about 6.0 dBic in the operating band, and the circularly polarized peak gain is about 7.6 dBic.