Design of a High-Efficiency and -Gain Antenna Using Novel Low-Loss, Temperature-Stable Li₂Ti₁–<i>_x</i>(Cu_1/3Nb_2/3)<i>_x</i>O₃ Microwave Dielectric Ceramics

Abstract

Microwave dielectric ceramics are vital for filters, dielectric resonators, and dielectric antennas in the 5G era. It was found that the (Cu_1/3Nb_2/3)⁴⁺ substitution can effectively adjust the TCF (temperature coefficient of resonant frequency) of Li₂TiO₃ and simultaneously increase its <i>Q</i> × <i>f</i> (<i>Q</i> and <i>f</i> denote the quality factor and the resonant frequency, respectively) value. Notably, excellent microwave dielectric properties (ε_r (permittivity) ≈ 18.3, <i>Q</i> × <i>f</i> ≈ 77,840 GHz, and TCF ≈ +9.8 ppm/°C) were achieved in the Li₂Ti_0.8(Cu_1/3Nb_2/3)_0.2O₃ (LTCN_0.2) ceramic sintered at 1140 °C. Additionally, the sintering temperature of LTCN_0.2 was reduced to 860 °C by the addition of 3 wt % H₃BO₃, exhibiting superior microwave dielectric properties (<i>ε</i>_r ≈ 21.0, <i>Q</i> × <i>f</i> ≈ 51,940 GHz, and TCF ≈ 1.4 ppm/°C) and being chemically compatible with silver. Moreover, LTCN_0.2 + 3 wt % H₃BO₃ ceramics were designed as a patch antenna and a dielectric resonator antenna, both of which showed high simulated radiation efficiencies (88.4 and 93%) and gains (4.1 and 4.03 dBi) at the center frequencies (2.49 and 10.19 GHz). The LTCN_0.2 + 3 wt % H₃BO₃ materials have promising future application for either 5G mobile communication devices and/or in low-temperature co-fired ceramic technology owing to their high <i>Q</i>, low sintering temperature, small density, and good temperature stability.