Research on ferroelectric materials for millimeter wave application

This technical report presents the results of the second six months of a research program on ferroelectric materials for phase control applications in millimeter wave radar systems. Originally a one-year program, this effort has been extended to fifteen months to take advantage of materials development activities in related programs. The major accomplishments in the current period include growth and preparation of several ferroelectric materials, and high frequency dielectric characterization of high purity single crystals of Sr.6Ba.4Nb206 (SBN:60). All systems examined to date exhibit high dielectric loss at millimeter wavelengths, the minimum being tan 11 0.3 near 40 GHz for a high purity SBN: 60 sample. The generality of this observation, when coupled with high sample-to-sample variability, suggests a commonly occurring extrinsic factor, such as growth defects, as the key element. How the frequency scale for polarization flucuations is tied to such extrinsic influences remains to be explored. A systematic study of the influence of defect structure on microwave dielectric properties of ferroelectrics is probably the most appropriate next step.