This paper presents a study of two longitudinal slots of same or different electrical lengths milled on a waveguide for series and shunt slot array antenna. Initially two elements series and shunt slot array are designed separately. Theoretical data for the scattering parameter have been obtained for two element series and shunt slot array antenna. The theoretical data have been compared with simulated data for validation the proposed design structures. After the validation, the total gain of the proposed design structures is simulated. The result found in different cases of slot array antenna behaves as either dual band antenna or single band within X-band. Dual band antenna is applicable for the multi frequency selective device for communication and single band antenna is applicable for the long distance data communication.