This paper presents our research work on designing a dual-band dual-polarized (DBDP) series-fed S/X-band shared aperture antenna (SAA) for synthetic aperture radar (SAR) applications. The proposed SAA DBDP X-band antenna is designed with the concept of series-fed 4-group 2x2 planar arrays with high impedance microstrip line feeding in both vertical and horizontal polarizations. By etching out the inner edge elements from 2x2 X-band subarrays in all the four-groups, the S-band element could be accommodated. The design evolution stages have been presented. The S-band (3.2GHz) is best suited for volumetric soil moisture estimation using SAR and X-band (9.3 GHz) best suited for surveillance SAR applications and grain size estimation. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The antenna with reflection coefficient lS11l < -10 dB has an impedance bandwidth 3.12-3.42 GHz (9.3% BW) in S-band and 9.2-9.36 GHz (1.72% BW) in X-band. The measured isolation lS21l between two different bands in the same polarization is better than 25 dB, and the isolation between two different bands in two orthogonal ports is better than 30 dB. Measured gain of the antenna at S-band is better than 8.5 dBi at V-port and H-port, and X-band is better than 11 dBi at either port. Measured side-lobe level (SLL) at S-band is better than -17 dB at either port, and X-band is better than -20 dB at either port. The overall size of the S/X-DBDP SAA is 100 x 100 x 1.6 mm³. Measured results of the S/X-DBDP SAA show good agreement with the finite integration technique (FIT) based computer simulation technology (CST) microwave studio.
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