A new design insight has been developed indicating possibilities of improved characteristics to be achieved in coax-fed microstrip antennas in terms of their polarization purity over the entire operating bandwidth. The investigation involves multiple configurations and variations of rectangular and circular patches to ensure conclusive inference. Their impedance profile including the probe parameters has been identified as the controlling factor to the cross-polarized (XP) profile over the band. Subsequently, a well-defined co-relation between the input and XP radiations has been established which leads to a theoretical model. Based on this understanding, an engineered feed with controlled reactance has been conjectured and proposed to achieve improved XP profile with increased polarization purity. This new finding and conjecture have been experimentally verified using multiple sets of prototypes operating in C-band. It confirms the predicted improvement in polarization purity over the entire bandwidth with a maximum of about 7 dB at the band-edge without imposing any change or degradation in other characteristics. © 1963-2012 IEEE.