A micro-strip predistortion circuit forr millimeter-wave millimeter-wave Travelling Wave Tube

With the development of communication technology, investigating predistortion circuit for Travelling Wave Tube (TWT) becomes more and more important. This paper analyzes the principle of nonlinearity generator based on the schottky diodes and the effects of the zero bias junction capacitor and series resistor of the diode Simulation Program with Integrated Circuit Emphasis (SPICE) model on the expansions of the circuit for the first time. The conventional micro-strip predistortion circuits, whose absolute or relative bandwidth are less than 1.8 GHz and 4%, work at below K band, and need isolators to match the input and output ports. Based on the Advanced Design System (ADS) software, it is designed that a micro-strip predistortion circuit for millimeter wave band TWT at center frequency 30 GHz, absolute bandwidth 2 GHz, and relative bandwidth 6.67%. The results of experiments show that the compressions variations of gain and phase are from 7.5 dB and 40°, 7.3 dB and 50°, 7.1 dB and 59°to less than 3.8 dB and 10°, 3.7 dB and 12°, 2.4 dB and 15°for the TWT without and with the linearizer at 29 GHz, 30 GHz and 31 GHz respectively. The two tones test results show that the iInput pPower bBack oOff (IPBO) are 17 dB, 18 dB and 18 dB for the TWT, but 12 dB, 9 dB, and 8 dB for the lLinearized TWT (LTWT), namely 5 dB, 9 dB, and 10 dB improvements with the linearizer at 29 GHz, 30 GHz, and 31 GHz respectively for the demand of 25 dBc Carrier to tTthird iIntermModulation (C/IM3) ratioin in communication system. The linearity of TWT has been is clearly improved with the linearizer, which serves as a great value for engineering application. © 2017, Science Press. All right reserved.