Wideband performance and size reduction of antennas are ostensible requirements of Wireless and Active Phased Array Radar Applications. The proposed paper aims to reduce the size of Planar Vivaldi Antennas to address these challenges by introducing defects in the ground plane of the antenna. The size of the Conventional Vivaldi Antenna specifically the width is reduced to 50% with the insertion of Defected Ground Structure (DGS). The effect of DGS was evaluated with the aid of four rectangular slots inserted on the two ground planes of the antenna (two on each ground plane). Optimal performance was achieved when these slots were inserted on the outer edges of the ground planes. Simulated results showed that the proposed Vivaldi Antenna offers 100% improvement in the impedance bandwidth even with the reduced size. Similarly, the proposed antenna offers an improved gain of 8 dB instead of 5 dB achieved from the basic model. The proposed Vivaldi antenna can easily be integrated with a stripline feed network for achieving wide bandwidth and narrow beam-width for radar and communication applications.