Passive Intermodulation Due to Self-Heating in Printed Transmission Lines

This paper proposes a mechanism by which third-order intermodulation distortion, due to self-heating, is generated in transmission lines. This work shows how transmission lines made of several materials, whose properties are independent of the electric and magnetic fields, can generate important levels of intermodulation distortion. A circuit model supported by finite-element simulations is presented to account for the temperature generation and also for its impact on the nonlinear performance. Closed-form expressions are used to calculate the generated intermodulation products and are derived from the circuit model and compared with simulations. Finally, measurements and simulations of different transmission lines are presented, showing very good agreement.