The RF predistortion is an effective method to improve the linearity of High Power Amplifier (HPA).To obtain a better linearity of the HPA

accurate amplitude and phase compensation are required.A novel RF predistortion circuit is proposed for the linearization of a Ka-band Travelling Wave Tube Amplifier (TWTA)

which consisted of a prepositive Variable Gain Amplifier (VGA)

a post VGA and a nonlinear signal generating module based on vector synthesis technique.When changing the gain of the two VGAs can realize the adjustment of the compensation range.Reasonably changing the bias voltages of the two branches in nonlinear generating module can adjust the compensation amount and also can independently regulate the amplitude or phase characteristic.The Third Order Intermodulation (TOI) of a Ka-band TWTA is improved 11.5 dB at 6dB output power back-off owing to the proposed RF predistortion linearizer.