ABSTRACT
This chapter examines the physical foundations of ferroelectricity and describes main properties of the ferroelectrics at microwave frequencies. Ferroelectric materials are under interest for practical applications at microwave technique. The ferroelectric inclusions are used as tunable components in multifunctional metamaterials. The traditional devices such as phase shifters for steerable antenna arrays, tunable resonators and tunable filters for telecommunication, and radar systems form the area of practical applications of the ferroelectric materials. The chemical nature and the crystallographic structure of high temperature superconductors (HTS) and ferroelectric materials are similar, and a success in HTS technology was used for a progress in the ferroelectric film technology. The chapter explores dielectric properties of the ferroelectric materials: appearance of spontaneous polarization, large value of dielectric constant, and dependence of the dielectric constant on temperature and applied voltage. Distinguishing features of ferroelectrics are spontaneous polarization, very high value of dielectric permittivity, dependence of dielectric permittivity on temperature, and dependence of dielectric permittivity on biasing voltage.
