For conventional quadrature-polarimetric (quad-pol) Synthetic Aperture Radar (SAR) systems, as cross-polarized (cross-pol) channels are influenced by the strong co-polarized (co-pol) range ambiguous returns, the range ambiguity levels of cross-polchannels are markedly reduced, which severely restricts the unambiguous swaths. A novel transmission scheme called a hybrid-polarimetric (hybrid-pol) mode is introduced to enhance the range ambiguity levels of cross-pol channels. This scheme improves the performance of cross-pol channels with regards to range ambiguity but deteriorates that of co-pol channels. Therefore, to further enhance the range ambiguity levels of quad-pol SAR systems, the Modified Azimuth Phase Coding (MAPC) technique based on hybrid-pol SAR systems is proposed in this study. By taking advantage of the MAPC modulation/ demodulation, the power of range ambiguities is transferred to the azimuth that is filtered by an optimized Wiener filter in the Doppler domain. The simulation results validate that the MAPC technique can markedly eliminate the range ambiguity of quad-pol SAR systems and extend the unambiguous swaths.