Novel ultra-low loss and low-fired Li8MgxTi3O9+xF2 microwave dielectric ceramics for resonator antenna applications

Abstract

Low temperature sintered Li8MgxTi3O9+xF2 microwave dielectric ceramics with x = 2−7 were developed based on a newly designed pseudo ternary phase diagram of the Li2TiO3–MgO–LiF system. Dense solid solution ceramics (of relative density >96 %) with cubic rock-salt structure, accompanied by a small amount of secondary phase MgO, were obtained in the temperature range of 800−925 °C. With increasing Mg2+ content, the value of εr decreased, whereas that of τf remained nearly constant, and the Q×f increased to a maximum at x = 5. The Li8Mg5Ti3O14F2 ceramic sintered at 875 °C exhibited superior microwave dielectric properties with εr= 16.8, Q× f= 119,700 GHz, and τf= −41.6 ppm/°C. The good compatibility with Ag electrodes highlights the promising prospects of this ceramic in low-temperature co-fired ceramic technology. Furthermore, a dielectric resonator antenna fabricated based on a Li8Mg5Ti3O14F2 ceramic exhibited an outstanding S11 of −34.7 dB and a broad bandwidth of 360 MHz at the desired resonant frequency of 5.98 GHz.