Dielectric properties of ceramics for microwave and millimeterwave applications

Dielectric Ceramics (DRs) have revolutionized the microwave wireless communication industry globally. The three key properties of ceramic dielectrics that determine their functionality at microwave and millimetrewave frequencies include relative permittivity (ε_r), unloaded quality factor Qu - the inverse of the dielectric loss (tanδ) and temperature coefficient of resonant frequency (τ_f). These microwave dielectric properties are affected by a number of factors. These includes tolerance factor, onset of structural phase transitions, dark core formation, processing conditions, raw materials and impurities, order/disorder behavior, compositional ordering, porosity, humidity, grain size, orientation of the crystallites, and grain boundaries. The data related to these factors is scattered. The main purpose of this review is to bring these together and present the effects of these factors on the microwave dielectric properties. Control of these factors is important for improvement in the microwave properties. This review would be very helpful to the novice researchers and technologists in the field.