Low-Loss Microwave Dielectrics for Different Frequency Ranges

Abstract

Depending on the operating frequency range of modern communication systems various microwave elements are required for effective operation of radio equipment. In this work potential ways of developing the microwave dielectric materials for different frequency ranges are discussed. It has been shown that temperature stable dielectrics with the permittivity of about 100, which are intended for the utilization in the decimetre wavelength band, can be developed by means of alio-and isovalent substitution in the cation sublattices of barium lanthanide titanates (BLTss) Ba 6−x Ln 8+2x/3 Ti 18 O 54 (Ln = La-Gd). The temperature behaviour of the permittivity and dielectric loss in the BLTss has been discussed in terms of both harmonic and anharmonic contributions to the phonons of the BLT crystal lattice. It has been shown that a slight deviation from the compositional stoichiometry in both A-site and B-site deficient perovskites Ba(M 2+ 1/3 Nb 2/3 )O 3 (M = Co, Zn, Mg) allows a prominent enhancement of their microwave quality factor (Q). As a consequence, new dielectrics with the extremely high quality factor (Qxf = 90 000-150 000 GHz), which are intended for the utilization in the centimetre wavelength band, can be developed. Some examples of the possible implementation of the developed materials are also discussed.

Effects of Y2O3 substitution on microwave dielectric properties of Ba(Co0.6Zn0.38)1/3Nb2/3O3 ceramics

“…According to published literature [5,27], we can rational assume that the s f value of BCZN phase is nearly 0 ppm/°C. When the doping amount increased from 0 to 0.06, the SEM (EDS) results above indicated that the increase of s f value can be owing to the relatively increasing amount of secondary phase Ba 8 CoNb 6 O 24 , reportedly having a positive s f value of nearly 14 ppm/°C [32], which can reasonably explain the rising trend of the s f value with increasing Y 2 O 3 doping in the Ba(Co 0.6 Zn 0.38 ) 1/3 Nb 2/3 O 3 solid solution. Therefore, the logarithmic mixing law can be used to explain the variation in of s f value.…”

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

“…In the decimeter wave band, high relative permittivity values (ε 100) along with the high thermostability of electro-physical properties and high Q u are required, which enables effective solution of microminiaturization problems. At the present time, solid solutions based on barium-lanthanide titanates (Ba 6−x Ln 8+2x/3 Ti 18 O 54 (Ln = La -Gd)), which have a potassium-tungsten bronze structure and ε r ≈ 80 -100, satisfactorily meet these requirements, but these materials are costly [3]. Therefore, new low cost materials with high permittivity (ε r 100) and Q u f o > 10,000 GHz with [6][7][8].…”

Influence of secondary phases on phase and microwave dielectric properties of new Ca2Ce2Ti5O16 ceramics

“…In the decimeter wave band, high permittivity values (εr ≥100) are required along with the high thermostability of electro-physical properties and high Qu are required, which enables effective solution of microminiaturization problems. At the present time, solid solutions based on barium-lanthanide titanates (Ba6-xLn8+2x/3Ti18O54 (Ln = La-Gd)), which have a potassium-tungsten bronze structure and εr≈ 80-100, satisfactorily meets these requirements, but these materials are costly [3]. Therefore, new low cost materials with high permittivity ( r ≥ 100) and Qufo > 10,000 GHz with f~0 ppm/ o C are essential for further miniaturization of the mobile handsets devices.…”