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An electrically large metallic cavity antenna with circular polarization (CP) is proposed in this letter. The aim is to increase the size of satellite antennas working in the Ku-band and other higher-frequency bands through low cost and easy fabrication. A brass C-band antenna prototype is designed, fabricated, and measured for concept verification. The overall dimensions of the antenna are 0.67λ0 × 0.67λ0 × 0.83λ0 at the working frequency. The resonant mode of the proposed cavity antenna is excited by a coaxial feeding probe, and circular polarization is realized by an inserted perturbation screw. The measured impedance bandwidth for | S11| ≤ -10 dB and 3-dB axial-ratio bandwidth are 1.02 GHz (6.07-7.09 GHz) and 320 MHz (6.59-6.91 GHz), respectively. The measured gain is 8.5 dBic across the whole 3-dB axial-ratio bandwidth. The measured 3-dB axial-ratio beamwidths at the central frequency are 150° and 148° in the xoz- and the yoz-planes, respectively, which is wide enough to cover the >; 0-dBi gain beamwidths of 120° for practical engineering applications. The measured and the simulated results show good agreement.