The paper reviews recent work at the Technical University of Denmark, aimed at developing a true shared aperture, i.e. dual-frequency (L- and C-band), wideband, dual-linear polarization microstrip antenna array for use in the next-generation of the Danish high-resolution, airborne, polarimetric synthetic aperture radar (SAR) system. The dual-frequency array concept adopted relies on the use of probe-fed perforated, stacked patches for L-band (1.2-1.3 GHz). Inside these perforations probe-fed, wideband stacked microstrip patches for C-band (4.9-5.7 GHz) are placed. Measured impedance and radiation pattern properties for this structure are reported.