Intermodulation Mitigation through Surrounding Impedance Manipulation

Intermodulation products in antennas and connectors are a serious problem for signal integrity and can significantly reduce the performance and capacity of mobile and satellite systems. The elusive nature of intermodulation, especially in metal contacts, leads to complexity in the analysis and understanding of the characteristics of these weak spurious signals. This paper investigates the effects of load and source impedances on third-order intermodulation (IM3). The analysis is conducted using a power series approach, which is validated through ADS simulations. Both the ADS simulation and the analytical results demonstrate that manipulating the impedance seen by the nonlinear element can improve IM3. Simulation results confirm that a 12 dB reduction in IM3 can be achieved when we increase the impedance seen by a nonlinear source (BAR64-02V PIN diode in our example) from 43 Ω to 100 Ω which has been verified by measurements. The applicability of the power series for analyzing IM3 is also discussed.