Low-Loss Microwave Dielectrics for Different Frequency Ranges

摘要

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_(1/3)~(2+)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 = 90000-150000 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.