Recent advances in metrology for the electromagnetic characterization of materials at microwave frequencies

An overview is presented of recent advances realized in the methods of measuring the complex permittivity, (ε^*=ε\´-jε"), complex permeability (μ*=μ\´-jμ") and RF surface impedance of electronic materials. We discuss a variety of different measurement techniques, including their relevant advantages and disadvantages. Nondestructive methods, that are important in material production quality control, are emphasized. Accurate measurements of low-loss materials (ε", μ"<0.01) require high-Q resonator techniques. Many examples of these are presented, including the TE_01p mode cylindrical cavity, the split post dielectric resonator for characterizing flat sheets, the dielectric rod resonator for measuring the RF surface resistance of superconductors, and the whispering gallery mode technique which provides the highest known sensitivity for dielectric loss measurements. Measurements of medium-to high-loss materials (ε", μ">0.1) are best performed using broadband free-space methods as well as transmission line techniques, such as waveguide, coaxial air line or the open-ended coax probe