This article presents a comprehensive study on reducing mutual coupling in a slotted waveguide antenna array (SWAA), operating in the X band. The objective is to limit such parasitic coupling effects on radiation pattern performances. Optimised choke structures are inserted between adjacent slots sub-arrays in order to control surface currents distribution. Simulation results exhibit a remarkable reduction on isolation between adjacent waveguides. This induces an overall performance improvement in terms of main beam and side lobes control. Furthermore, using field calculator on HFSS™, the efield levels of each slot are extracted. The plus points and drawbacks of the choke structure on the radiation pattern are then explained.