In this work, a dual-band dual-polarized (DBDP) S/X-band multilayer shared aperture antenna (SAA) for airborne synthetic aperture radar (ASAR) applications. The proposed multilayer SAA DBDP S-band antenna is designed with the concept of the cross-shaped patch with proximity coupled feeding in both vertical and horizontal polarizations and X-band antenna design is with aperture coupled square patch arranged as a 4 × 4 planar array for high gain and narrow beamwidth with corporate feeding for good radiation characteristics as array design. The S-band (2.7 GHz) is best suited for soil moisture; X-band (9.7 GHz): mainly for snow and cold regions, and for disaster monitoring. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The S/X-DBDP SAA has fractional bandwidth of 7.7% at 2.7 GHz and 4.8% at 9.7 GHz, respectively, and the port isolation between S- and X-bands is higher than 25 dB. The design exhibits an SLL (S-band: −13 dB and X-band: −15 dB), high gain (S-band: 8.48 dBi and X-band: 21.8 dBi). The overall size of the S/X-DBDP multilayer SAA is 125 × 125 × 8 mm3. The SAA is best suited for large size array antenna for ASAR applications. © 2021 Wiley Periodicals LLC.