The analytical expression of the successful probability of using an IRST sensor cueing a 3D radar is derived for a co-located radar-IRST system.With the analytical expression

the successful cueing probability can be easily obtained.The relations between the successful cueing probability and the parameters are also given.Numerical calculation of the successful cueing probability is conducted for several cases and the results verify the relations of the successful cueing probability with the parameters.Discussions are also made.The conclusions presented in this paper are useful in designing co-located radar-IRST cueing systems.