Regulation of the temperature stability in ordered olivine microwave dielectric ceramics with low loss for dielectric resonant antenna

Olivine-type A₂BO₄ ceramics possess a low permittivity (ε_r) and low dielectric loss, contributing to a high quality factor (Q×f). However, the large negative temperature coefficient of the resonant frequency (τ_f) restricts their practical applications. In this work, we prepared a series of CaYGa_1−xAl_xO₄ (x = 0–1) ceramics with low ε_r values via solid-state sintering. By controlling the evolution of orthorhombic olivine to the tetragonal perovskite-like structure (K₂NiF₄) and the ordered regulation of the A-site, an ultralow loss (tanδ = 1.38×10⁻⁴, Q×f = 125,530 GHz, and f = 17.3 GHz for x = 0) and a nearly zero temperature coefficient (τ_f = −0.5 ppm/°C for x = 0.9) were achieved. The significant changes in the dielectric properties (ε_r = 8.3–16.2, Q×f = 125,530–50,660 GHz, and τ_f = −50.9 to 2.9 ppm/°C) of these ceramics are primarily influenced by the characteristics of the second phase, ion polarization, ion order and disorder, and the chemical bonds resulting from structural evolution. Furthermore, a cylindrical dielectric resonator antenna (CDRA) was designed using an ultralow-loss CaYGaO₄ ceramic, achieving a high gain (5.36–6.15 dBi) and efficiency (> 90%) in the bandwidth region (5.065–5.747 GHz), thereby enhancing the efficiency and quality of 5G communications. This work advances the development of control strategies for high-performance dielectric ceramics and dielectric resonator antennas in high-frequency communications.