LAUSR

In this paper, a novel wideband circularly polarized (CP) slot antenna and its array are presented. The antenna element consists of a C-shaped slot and a 50- $\Omega $ microstrip-fed port to achieve left-hand circular polarization. Both the impedance bandwidth (IBW) and the 3-dB axial ratio bandwidth (ARBW) are greatly broadened by off-center microstrip-fed sword-shaped structure. A $2\times 2$ array prototype based on the proposed CP element is also designed. Sequential rotation microstrip-feeding structure is used to excite four antennas and to realize good symmetric unidirectional radiation. To verify this design, both the CP antenna element and $2\times 2$ array are fabricated and measured. The measured results of the antenna element exhibit an IBW of 132% (0.85– $4.15~GHz$ ) and an ARBW of $95.7{\%} (1.20-3.40$ GHz). The measured ARBW and IBW of the $2\times 2$ antenna array are about 108.3% (1.10– $3.70~GHz$ ) and $100{\%} (1.15-3.45$ GHz), respectively. And the measured peak gain of the antenna array reaches 13.4 dBic. The proposed antenna is very suitable for CP applications in L/S bands.