Passive Intermodulation Generation on Printed Lines: Near-Field Probing and Observations

The phenomenological mechanisms of passive intermodulation (PIM) in printed lines have been explored by mapping intermodulation products generated by the two-tone traveling waves in microstrip lines. Near-field probing based upon a commercial PIM analyzer has been employed for identification of the PIM sources in printed lines. The results of extensive near-field probing provide the direct experimental evidences of cumulative growth of the intermodulation products in the matched uniform microstrip lines and reveal the fundamental role of the nonlinear scattering by the lumped nonlinear inclusions in the intermodulation production. The distributed nature of the PIM generation in microstrip lines has been conclusively demonstrated and comprehensively described in terms of the four-wave mixing process that proved to be fully consistent with the results of experimental observations of third-order PIM products on the matched and mismatched microstrip lines. © 2006 IEEE.

Passive intermodulation in finite lengths of printed microstrip lines

This paper addresses the theoretical aspects of passive intermodulation (PIM) generation in printed transmission lines. In order to elucidate the mechanisms of PIM generation, a new model of the transmission line length with distributed nonlinearity is proposed. The developed model has been validated by the near-field measurements of PIM product distributions along the microstrip lines. The contributions of nonlinear mixing, power dissipation, and load matching to PIM products have been analyzed in detail. The obtained results reveal the fundamental properties of PIM generation in finite lengths of printed lines with distributed non-linearity and identify possible means for PIM mitigation. It was shown for the first time that the reverse PIM products in a matched transmission line with distributed nonlinearity are generated due to nonlinear scattering. © 2008 IEEE.

Effects of Interface Conditions and Long-Term Stability of Passive Intermodulation Response in Printed Lines

An experimental investigation of the effect of conductor-to-substrate interface on distributed passive intermodulation (PIM) generation in printed microstrip lines has been undertaken using the custom-designed microwave laminates with removed surface bonding layers and with the commercial adhesion promotion applied to the conductor underside. The study of long-term stability of PIM performance of the printed circuits is reported for the first time. The comprehensive measurement results, observations of the selfimprovement of the PIM performance and the effect of panel bending on PIM generation in printed boards with different finishing are presented. A consistent physical interpretation of the observed phenomena is proposed. The results of this study provide new important considerations for the design and characterisation of low-PIM printed circuits.

Artificial Impedance Surfaces for Reduced Dispersion in Antenna Feeding Systems

An impedance surface is presented that reduces the dispersion experienced upon propagation of broadband pulses within rectangular waveguides. The surface impedance is selected so that, within a frequency range, the transverse resonance condition is satisfied for longitudinal wavenumber that varies linearly with frequency. A synthesis procedure for practical surface topologies consisting of periodic dipole arrays is described. An example involving a finite structure is employed to illustrate the reduced dispersion. Numerical simulation results obtained from in-house mode-matching method as well as HFSS are presented. A prototype is fabricated and tested experimentally validating the theoretical predictions.