A single-pole double-throw (SPDT) strip-line switch has been designed to switch 10 watts CW power in the frequency range of 11.6 ~ 12.8 GHz. The switch has been fabricated on a polystyrene (Cuflon) substrate of a size 20.0×30.0×1.524-mm. Circuits were designed to cover the 10% frequency range to realize a minimum isolation of 23.5dB, a maximum SWR of 1.8, and maximum insertion loss of 1.8dB.