A Design of Broadband Circularly Polarized C-Shaped Slot Antenna with Sword-Shaped Radiator and Its Array for L/S-Band Applications

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-Ω 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 × 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 × 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 × 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.