Microstrip patch antennas are very attractive due to their low profile and simple construction capability. But their disadvantages include narrow bandwidth, low gain, and surface wave propagation in a dielectric substrate. In dielectric substrates, a wave propagates that amplifies the mutual coupling between the elements and thereby reduces antenna gain and bandwidth. When space is scanned by the main beam, the surface wave propagates at a particular angle and the strong mutual coupling between the array elements results in impedance mismatch and, as a result, the power is reflected to array input. This angle is called "scan blindness angle of the phased array antenna". Reducing the surface wave can move the blind angle to larger angles and, as a result, array scans the wider region. In the past few decades, different methods have been used to remove surface wave in phased array antennas.In this thesis, first, the angle of the blindness and the surface wave have been introduced. The floquet analysis method of periodic structures is then used to determine the blind angle in a phased array antenna with uniform excitation. Analytical and numerical methods for analysis of EBG structures are presented. Then, a fourth order Hilbert curved EBG structure is designed and simulated to resonance and creation the band gap in X band. This structure does not require vias and therefore has a simpler construction capability. Five rows of proposed EBG have been placed between two microstrip patch antennas and it has been observed that the mutual coupling decreases by about 20 dB. An array of 9 × 7 elements is simulated. The results show that the existence of the EBG structure between the antenna elements can eliminate the scan blindness in 40 degrees. Keywords Phased array antenna, Electromagnetic bandgap structure, Scan blindness, Surface wave