Regulation of the temperature stability in ordered olivine microwave dielectric ceramics with low loss for dielectric resonant antenna
Huaicheng Xiang, Yang Zhou, Junqi Chen, Ning Zhang, Wu Xiaoyu, Ying Tang, Liang Fang
Abstract
Olivine-type A<sub>2</sub>BO<sub>4</sub> ceramics possess a low permittivity (<em>ε<sub>r</sub></em>) and low dielectric loss, contributing to a high quality factor (<em>Q×f</em>). However, the large negative temperature coefficient of resonant frequency (<em>τ<sub>f</sub></em>) restricts their practical applications. In this work, we prepared a series of CaYGa<sub>1-<em>x</em></sub>Al<em><sub>x</sub></em>O<sub>4</sub> (<em>x</em> = 0–1) ceramics with low <em>ε<sub>r</sub></em> using the solid-state sintering method. By controlling the evolution of the orthorhombic olivine to the tetragonal perovskite-like structure (K<sub>2</sub>NiF<sub>4</sub>) and the ordered regulation of the A-site, an ultra-low loss (tan<em>δ</em> = 1.38<em>×</em>10<sup>-4</sup>, <em>Q×f</em> = 125,530 GHz, and <em>f</em> = 17.3 GHz for <em>x</em> = 0) and a nearly zero temperature coefficient (<em>τ<sub>f</sub></em> = -0.5 ppm/°C for <em>x</em> = 0.9) were achieved. The significant changes in the dielectric properties (<em>ε<sub>r</sub></em> = 8.3–16.2, <em>Q×f</em> = 125,530–50,660 GHz, and <em>τ<sub>f</sub></em> = -50.9– +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 ultra-low-loss CaYGaO<sub>4</sub> 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.