A new approach based on the incorporation of Zshaped defected ground structure (DGS) in microstrip antenna (MSA) for improving impedance matching and cross polarization (XP) performances is proposed in this paper. Through detail analysis of the surface current densities, and input impedance, the proposed DGS is integrated into a rectangular MSA (RMSA) to realize flat relative XP reduction of 22 dB in the H-plane around broadside angular range of ±60°. Further, an equivalent circuit model (ECM) for the proposed antenna is introduced by considering the mutual coupling in between the DGS and patch and the model is verified using circuit-system-EM cosimulation software, Advanced Design System (ADS). A prototype has been fabricated and tested for the validation of simulated results and it shows good agreement with each other. The antenna operates over 2.32-2.58 GHz with good far-field radiation characteristics and a peak gain of 2.8 dBi at the resonating frequency 2.4 GHz. Hence, the proposed design can be useful for the IEEE 802.11b applications. © 2019 RADIOENGINEERING.