A W-band broadband frequency tripler was formed by anti-parallel Schottky-barrier diode pair. The input signal was fed in by a WR-28 waveguide-to-microstrip transition, and the output signal was fed out by a reduced-height WR-10 waveguide. For the input power of 5dBm, the output power was 0.81±1.80dBm and the second harmonic rejection was greater than 25dBc in the whole W-band. This tripler can be used to extend Ka-band signal source to W-band.