Composite tunable materials with low loss-factor at microwaves

This paper addresses the theory the tunable behavior of the nonlinear dielectric composites, consisting of an electrically tunable ferroelectric material mixed with a linear, low dielectric permittivity, low loss dielectric. It is theoretically shown that the tunable performance of ferroelectrics can be slightly improved by mixing them with linear dielectrics and that, contrary to the general "intuitive belief, the origin of this improvement is due to a slight increase of tunability rather than due to a decrease of the loss tangent. The experimental data on electrical properties of diluted barium strontium titanate (BST) are discussed in the context of the theoretical results.