Theory and Time-Domain Simulation of Third-Order Intermodulation Suppression by Signal Injection

This letter reports a new theoretical analysis of third-order intermodulation (IM3) reduction in nonlinear communication amplifiers by signal injection. On the basis of well-known Volterra series analysis, we put forward a general model that can analyze both the qualitative and quantitative effects of injected signal parameters on output IM3s, which previous literatures failed to achieve. Our theory can directly calculate the optimal amplitude and phase of single injected signal and points out the duality for some dual-signal injections which can help reduce their parameter scanning complexity from 4-D to 2-D. These conclusions are in good agreement with the simulation of two traveling wave tube (TWT) amplifiers by 3-D-FDTD-PIC code and CST and MTSS. Our work proposes an original analysis about how to adjust injected external signals to obtain best IM3 cancellation in communication systems, and boosts the research efficiency for new signal injection techniques from a novel perspective.