Abstract: In order to satisfy some special demands for detection and recognition to the guiding radar of Air Defense Missile Weapon System (ADMWS) using an active radar seeker, an analysis method of planar slotted array antennal RCS is stressly studied based on the theory of the antennal electromagnetic scattering mechanism. An electromagnetic scattering model of the antennas is established, and it introduces the detailed calculation procedure. The influences to antennas RCS of factors such as antenna size, frequency and quantity of slot etc are detailedly discussed. The simulation result shows that RCS of radar antenna is biggish and possesses obvious periodicity, and the range characteristic and period characteristic can be regarded the important basis of recognition. The work is meaningful for the research on detection and recognition algorithm for ground-based radar stations.