Recently, gap waveguides have been shown as a potential alternative to convenational waveguides in the millimeter-wave band. Until now, groove gap waveguide (GGW) has been studied through direct correspondence with rectangular waveguide with the same physical dimensions. However, there have been observed differences in the above cutoff propagation characteristics between these two waveguide types. Furthermore, the behavior of GGW below cutoff remains unknown. This work presents a discussion of both below and above cutoff propagation characteristics of GGW, and introduces a simple model that explains the observed GGW behavior and establishes well its propagation characteristics. Two thru-reflect-line calibration kits have been manufactured, and the measurements have good agreement with the proposed analysis model results.

This letter gives the first report of a planar phase plate structure based on frequency selective surface (FSS) technology for the generation of helical far-field radiation patterns with circular polarization properties. The unit cell of the structure comprises two orthogonal split-ring resonators designed to ensure 180 phase shift between orthogonal transmission coefficients. This property is exploited to obtain progressive rotational phase shift within the structure and thus synthesize 360 spiral phase profile. Measured far-field radiation patterns demonstrate spiral phase front generation for 10-GHz circularly polarized waves transmitted through the structure.

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 nonlinearity 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.

This paper proposes a substrate integrated waveguide (SIW) cavity-based method that is compliant with ground-signal-ground (GSG) probing technology for dielectric characterization of printed circuit board materials at millimeter wavelengths. This paper presents the theory necessary to retrieve dielectric parameters from the resonant characteristics of SIW cavities with particular attention placed on the coupling scheme and means for obtaining the unloaded resonant frequency. Different sets of samples are designed and measured to address the influence of the manufacturing process on the method. Material parameters are extracted at V - and W -band from measured data with the effect of surface roughness of the circuit metallization taken into account.

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.