Simultaneous Suppression of IMD3 and IMD5 in Space TWT by IMD3 and 2HD Signal Injection

Dongming Zhao,Xiaoxu Shi,Kewen Xia,Shi Li,Huijuan Liu

doi:10.1155/2017/4721048

Abstract

This paper presents a signal injection technology showing significant reductions in both 3rd-order and 5th-order intermodulation distortions (IMD3 and IMD5) in space traveling wave tube (STWT). By applying the IMD3 to the IMD5 ratio (TFR) as measures of location, the simultaneous suppressions of IMD3 and IMD5 in TWT are achieved by second harmonic distortion (2HD) and IMD3 injection. According to the research on theoretical analysis and computer simulation, the optimum amplitude and phase parameters of the injected signal for maximum simultaneous suppressions are obtained. Then an experiment system is established based on vector network analyzer, optimum TFR are 2.1 dB and 12.5 dB, respectively, by second harmonic and IM3 injection, and the output powers of IMD3 and IMD5 were decreased. TFR with IMD3 injection is smaller than that with second harmonic injection in STWT, and the experiment system is more straightforward and easy to operate. Thus, the IMD3 injection performs better than that of second harmonic injection to suppress IMD5s for the narrow-band STWT.

Highlights

Traveling wave tube (TWT) amplifier is widely used in the fields of communication, signal processing, radar, electronic warfare, and so forth
There are some new research results about signal injection including the improvement of the fundamental signal power of TWT by harmonic injection [4, 12], the harmonic and intermodulation distortions associated with two-tone modulation [13], the suppression of IMD3 by harmonic injection [14], and the particle swarm optimization algorithm (PSO) which are applied to suppress IMD [15, 16]
IMD5 (3ω1−2ω2 and 3ω2−2ω1) are in the working frequency band of space traveling wave tube (STWT), the effect on fundamental signal is next to IMD3, and both of them are the main performance of nonlinear distortion in STWT

Summary

Introduction

Traveling wave tube (TWT) amplifier is widely used in the fields of communication, signal processing, radar, electronic warfare, and so forth. In other areas of electronic device, An optoelectrical predistortion optical transmitter system is designed by Lee et al [8] This presents that the simultaneous suppressions of IMD3 and IMD5 are achieved by choosing an appropriate bias current and RF input power for the LD. There are some new research results about signal injection including the improvement of the fundamental signal power of TWT by harmonic injection [4, 12], the harmonic and intermodulation distortions associated with two-tone modulation [13], the suppression of IMD3 by harmonic injection [14], and the particle swarm optimization algorithm (PSO) which are applied to suppress IMD [15, 16]. Initial power and initial fundamental frequency represent input power and frequency of two-tone fundamental signal, they are variable, and the initial power and frequency variation of fundamental signal can influence output power of FUN, IMD3, and IMD5 under optimum injection and without signal injection

Theoretical Analysis

Simulation Results and Discussions

20 IMD5 signal

Experiment and Analysis

Conclusion