Objectives: This article manifests a study of high peak gain of a slotted array waveguide antenna. At first, two similar slot lengths 2-elements shunt slotted array antenna structures (i.e. Case-1) and two dissimilar slot lengths 2-elements shunt slotted array antenna structures (i.e. Case-2) are designed one by one. Methods/Statistical Analysis: The Multiple Cavity Modeling Technique (MCMT) has been applied in both cases of structural antennas. The scattering parameters (i.e. |S11| and |S21|) data have been computed for both cases of 2-element shunt slotted array antenna. The MCMT |S11| and |S21| data graphs have been compared with Ansoft High Frequency Structure Simulator (HFSS) simulated data graphs. Comparison results signify that a slight difference between computed and simulated data. Findings: Subsequently, the HFSS simulated gains total of the both cases of design structures antenna are obtained. The outcome found in 2-element shunt slotted array with similar slot length gains higher total rather than dissimilar slot length 2-element shunt slotted array antenna. In order to achieve further increases in gain a 2-elements lotted array antenna up to optimal point was extended up to seven slots. Analysis was done to compare the results with theoretical and simulated HFSS results. Application /Improvement: The antenna finds its application in high speed data communication system in the area of aircraft.