Abstract: Ka-band coupled-cavity traveling wave tube amplifiers have been developed for military radar application requiring high power, moderate bandwidth and light weight.The design features and measured performance characteristics of these devices are presented and the basic components of TWT are illustrated. The technology advancement achieved in the radar programs is being leveraged to design Ka-band amplifiers that surpass power limitation of existing solid state or helix TWT systems. The Ka-band coupled-cavity TWT technology has demonstrated output power, bandwidth and weight advantages in high-resolution military radar application.