Ultralow-Permittivity and Temperature-Stable BaCaMgAlSiO Dielectric Ceramics for C-Band Patch Antenna Applications.

Ca-substituted BaCaMgAlSiO ceramics were prepared to explore the relationships among their crystal structural parameters, phase compositions, dielectric properties, and coefficients of thermal expansion and applications in C-band antenna. The maximum solubility of BaCaMgAlSiO was located at = 0.25, and BaCaMgAlSiO ceramics (0 ≤ ≤ 0.25) crystallized in the space group 6/. In BaCaMgAlSiO single-phase ceramics, ε was dominated by ionic polarizability and "rattling effects" of Ba and Al(2); × was controlled by the roundness of [SiAlO] inner rings and total lattice energy; and τ was affected by the bond valence of Si/Al(1)-O(1). Notably, the low average coefficients of thermal expansion (2.668 ppm/°C) at -150 °C ≤ ≤ 850 °C and near-zero coefficients of thermal expansion (1.254 ppm/°C) at -150 °C ≤ ≤ 260 °C were achieved for the BaCaMgAlSiO ( = 0.1) ceramic. Optimum microwave and terahertz dielectric properties were obtained for the BaCaMgAlSiO ( = 0.1) ceramic with ε = 5.80, × = 31,174 at 13.99 GHz, τ = -7.10 ppm/°C, and ε = 5.71-5.85 at 0.2 THz ≤ ≤ 1.0 THz. Also, the BaCaMgAlSiO ( = 0.1) ceramic substrate had been designed as a C-band patch antenna with a high simulated radiation efficiency (87.76%) and gain (6.30 dBi) at 7.70 GHz (|S| = -38.41 dB).