Abstract: According to the design of 3 mm-wave radar, an amplifier-chain scheme of the coherent pulsed transmitter is proposed. The chain consists of a fundamental injection-locked harmonic Gunn oscillator, a CW IMPATT oscillator and two pulsed IMPATT oscillators in cascade. In order to overcome the effect of the leak signal in the system, a new technique of suppressing the leak in the intervals of pulse by altering the frequency is created and realized in success. The developed transmitter provides the output of 5 W peak power and 30 ns pulse-width in 3 mm-wave with the input of 2 mW signal in 6 mm-wave.