Abstract: The design of a tri-band dual-polarized (TBDP) shared-aperture microstrip array for SAR applications is introduced. This TBDP array operates at X, S and L bands with a frequency ratio of 8:2.8:1. It composes of two L/S and L/X dual-band dual-polarized (DBDP) shared-aperture sub-arrays and one L-band dual-polarized (DP) sub-array. Its measured impedance bandwidth and radiation patterns agree well with the simulated results at each band. The|S₁₁|≤ 10dB bandwidths of 13.4%, 14.8% and 16.8% are measured at L, S and X bands, respectively, and the array isolation of better than 37dB is measured in all bands. The measured radiation patterns show that the cross-polarization level is lower than -30 dB within main lobe regions for all three bands and the scanning capacity is better than±25° in both S-and X-bands. This array synthesis method may be further extended to realize shared-aperture dual-polarized arrays with more than three bands.