New Broadband Predistortion Linearizer Using Balanced Circuits Structure for Satellite TWTAs

The power amplifies is a key component influencing the power efficiency of communication system. The travelling wave tube is widely used in satellite system because of its high efficiency, apposite weight and broadband characteristic, but its strong nonlinear characteristic generates intermodulation distortion, which degrades the data quality of transmitted signal and causes interference in adjacent channels. The analogue predistortion structure using Schottky diodes could improve the linearity well, but parasite element in the Linearizer limits predistortion broadband, reluctant to satisfy the growing high volume data transmission requirement. This paper presents a new balanced structure of Linearizer for the travelling wave tube amplifier. We have analyzed the model of linearizer and the TWTA and used to calculate the intermodulation distortion and optimize the Linearizer nonlinear expansion characteristic. A frequency bandwidth of 1.2 GHz Linearizer has been demonstrated with a K-band TWTA between 19.8 and 21.0 GHz. The measurement result shows that the linearizer delivers about 2~6dB of gain expansion and 20~60 degrees phase shift expansion, and the cascaded LTWTA shows good linearity improvement of 17.8dB at 6dB input power back off point