Design of a steerable launcher for the ECH system on KSTAR

105/140Ghz dual frequency gyrotron is used in KSTAR tokamak for an electron cyclotron resonance heating (ECRH). The ECH launcher consists of a fixed mirror, a steering mirror, cooling systems and some mechanical component for a steering mirror. We have designed the fixed ellipsoidal focusing mirror for an efficient heating and localized control. The beam radius using the existing ECH launcher system is about 45 mm at the resonance layer. On the other hand, the modified launcher mirror reduces the beam size at the resonance layer for incident RF beam to 38 mm. The design results showed good agreement compared with the computation and simulation results. Since the distance between the corrugated waveguide and the fixed focusing mirror is fixed, it is difficult to more reduce the beam size. However, reduced beam size is small enough to localize MHD control and heating