In this paper, a circularly polarized antenna for Synthetic Aperture Radar (SAR) application is presented. The antenna is proposed to be implemented for the airborne SAR and the spaceborne SAR. To enhance the bandwidth of the antenna, the Circular-Ring-Slot (CRS) technique is implemented on the ground plane and in a square slot in the centre of the patch. In this antennas design, the model of the slot on the radiator is also investigated. The antenna is printed on NPC-H220A substrates with the dielectric constant of 2.17 and thickness of 1.6 mm. The resonant frequency of the antenna design sets at 9.4 GHz with the minimum requirement of the bandwidth of 800 MHz. The antenna design is produced under the -10 dB bandwidth of reflection coefficient, S11 of approximately 27% (8.2 GHz-10.76 GHz) and left-handed circular polarization (LHCP). The gain of the antenna is 6.5 dBic and 12.7% (8.8 GHz-9.84 GHz) for the axial ratio bandwidth (ARBW). This paper includes the description and presentation of the completed discussion.
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