Abstract: To meet the demands for miniaturization and lightweight design in applications such as modern satellite communication systems, 5G, and RIS, a compact, dual-band circularly polarized feed antenna operating in the K/Ka bands is proposed. This antenna modifies the current distribution by perforating specific locations on the partition, thereby expanding the impedance and axial ratio bandwidth, with a relative bandwidth reaching 57.14%. Through appropriate filter selection and joint optimization design, as well as the choice of partition perforation parameters, wideband circularly polarized radiation is achieved while maintaining high isolation between antenna ports and reducing physical length. Simulation and measured results show that the antenna has a return loss S11 of less than -13 dB within the K (17.5-21.5 GHz) and Ka (27.5-31.5 GHz) bands, the in-band axial ratio is less than 3 dB, gain ranges from 7.88 to 12.70 dB, and port isolation exceeds 42 dB and 29 dB in the K and Ka bands, respectively. Measured polarization isolation at 20 GHz and 30 GHz is greater than 20 dB. The overall size of the feed antenna is compressed to only 61 mm × 21 mm × 21 mm. Compared with existing results, under the same conditions without including the radiation horn, the length is reduced to 51 mm, achieving a size reduction of 43%; when including the radiation horn, the reduction reaches 65%. The measured and simulated results show good consistency.