Cross polar (XP) radiations in an inset-fed microstrip line-fed patch are mainly caused by the unwanted fields radiated from the transition between the feed and the patch, and due to the higher order modes in the patch cavity. The XP isolation has been significantly improved by a new and simple configuration of defected ground structure (DGS). The DGS is designed to act as magnetic dipoles and thus compensates the unwanted XP radiations. This concept has been validated by inset fed antenna designs in S- and C-bands. The results indicate co-to-cross polarized isolation of more than 35 dB with DGS, compared to about 20 dB for a patch with conventional ground plane. The DGS does not affect other parameters such as impedance bandwidth and peak gain of the antenna. This design should be ideal for wireless and satellite communication applications where large XP isolation is required. © 2019 URSI. All rights reserved.