Abstract A new method of transmit pattern synthesis for Secondary Surveillance Radar (SSR) is presented. This method is concerned with an active phasedarray antenna. A cosine on pedestal excitation for aperture distribution is used to synthesized the desired directional pattern, which is used to transmit the P1 and P3 pulse for interrogation. Using stationary phase method, the phase function over aperture on the specified aperture amplitude distribution is obtained and the desired pattern to transmit the P2 pulse is synthesized for Interrogation Side Lobe Suppression (ISLS). The antenna and relevant equipment which transmits only the P2 pulse is saved.