In this paper, we described the study on back-radiation level improvement of IFF antenna after briefly describing a design of IFF antenna to distinguish the target as the sub-antenna of surveillance radar. The proposed IFF antenna was minimized a size with use all-in-one power divider as a two-channel IFF antenna forming sum and difference pattern. The method for back-radiation level reduction was studied, and the identified method through the simulation confirmed the decrement throught the measurement.