One of the most widely used antenna in military radar is phased array antenna for tracking targets.with taking beam main away angle of scanning broadside, we encounter with two problem, One is that grating lobes close to the antenna radiation pattern visible region, Second, return loss and side lobe level is degraded in comparison with isolated element due to the mutual coupling between antenna array elements. scanning angle of array antenna is limited by these problems.In this thesis, three Evanescent mode open-ended waveguide antenna is designed by three array elements, 1-post(inside the antenna), 2-dielectric layer(In front of the antenna) and 3-combination post and dielectric layer in X-band. Minimum realized gain of three array element is 4dB and their impedance bandwidth is 8.5%, 16.6% and 30.7% respectively. Back Lobe Level (BLL) of antenna number one is decreased 5.5dB by displacing PEC plane from antenna back. By placing PEC around of antenna aperture, back lobe level is decreased 2.8 dB and -13.3 dB is achieved.This element is arranged by lattice brick and 25dB taylor distribution in circular planar array with radius of 7.5 Cm. different dielectric layer is placed in front of array in order to decreasing return loss of array element.The best result is achieved by Rogers Ro4003 dielectric with 0.406mm thickness and 1mm distance from array aperture. Active reflection coefficient, gain and SLL degradation of array are good until angles in any scan plane. These angles in H,D and E scan plane are , and respectively.number of elements with return loss less than 10dB are only 10% of all array element in scan volume mentioned above. In E and H plane Gain degradation is about 1dB and in D plane is about 2dB. SLL increase of phase array antenna in E and H plane is about 3.5dB and final values are -20.2dB and -20.1dB respectively. SLL increase in D plane is about 2.5dB and final value is -22dB. Bandwidth of centeral element of array in scannig plane is higher than 9dB, gain of array is 30.2dB and resolution is . Keywords Phase array antenna, Mutual coupling, Wide angle impedance matching, Evanescent mode open-ended waveguide antenna.
