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Novel BaCa2M3O9 (M = Si, Ge) microwave dielectric ceramics were prepared via solid‐state reaction with sintering at 1125°C–1275°C for 5 h. Single‐phase BaCa2M3O9 (M = Si, Ge) ceramics were obtained according to stoichiometry. The single‐phase BaCa2Ge3O9 ceramic was confirmed through Rietveld refinement and high‐resolution transmission electron microscopy/selected area electron diffraction and synthesized for the first time. The BaCa2M3O9 (M = Si, Ge) exhibited a triclinic structure with a P1¯$\bar 1$ space group and good microwave dielectric properties. The εr, Q × f, and τf values of BaCa2M3O9 (M = Si, Ge) ceramics are mostly dominated by the relative density, ionic polarizability, relative covalence, and bond energy of M–O bond, respectively. A high Q × f value (61 800 GHz at 16.3 GHz) was obtained in BaCa2Ge3O9 ceramic due to its high rc (Ge–O) and low intrinsic dielectric loss. The BaCa2Si3O9 ceramic exhibited small |τf| value (‒36.4 ppm/°C) due to its large ESi‐O. Excellent microwave dielectric properties (εr = 8.31, Q × f = 61 800 GHz, and τf = ‒58.7 ppm/°C) were obtained for the BaCa2Ge3O9 ceramic. [ABSTRACT FROM AUTHOR]

The dielectric properties of a Ga‐based melilite type ceramic Sr2Ga2SiO7 via theoretical prediction based on far‐infrared spectroscopy and experimental measurement by the Hakki–Coleman method were studied in this work. Dense and single‐phase ceramics were fabricated via solid‐state reaction at 1330°C and exhibited comprehensive microwave dielectric properties (εr ∼ 7.6, Q × f ∼ 23 600 GHz, and τf ∼ −35.2 ppm/°C) at 14.3 GHz. Chemical modifications were proposed to adjust the thermal stability and reduce the densification temperature. By adding 10 mol% CaTiO3, the negative τf can be compensated to a near‐zero value of −3.8 ppm/°C. The densification temperature was reduced to 940°C by adding 3 wt.% LiF. A patch antenna was designed using Sr2Ga2SiO7 ceramic with a high radiation efficiency of 99.1% and a gain of 2.788 dBi at the center frequency of 4.371 GHz. All results indicate that the Sr2Ga2SiO7 ceramic has promising application potential for 5G wireless communication technology. [ABSTRACT FROM AUTHOR]

A novel high-efficiency dielectric patch antenna was fabricated using Sr 3- x Ca x V 2 O 8 ceramics. A typically temperature-stable Sr 3- x Ca x V 2 O 8 was achieved by tailoring the Ca2+ substitution to 30 mol% (x = 0.3), where well-balanced microwave dielectric properties were obtained (a near-zero value of +5.2 ppm/°C, a low ε r ∼ 13.4, and a moderate Q × f ∼ 18,500 GHz). To manifest the application potentiality in wireless communication, a patch antenna was fabricated from the x = 0.3 ceramic based on the simulated result using the CST Microwave Studio software, and it showed a high simulated radiation efficiency (99.7%) and a gain (5.35 dBi) at 3.421 GHz. All results indicate that the Sr 3- x Ca x V 2 O 8 ceramics have promising application potential for 5 G technology due to their prominent microwave dielectric properties, lightweight, and low cost. [ABSTRACT FROM AUTHOR]

High-speed signal propagation systems require dielectric ceramics with low relative permittivity (ε r) and a high-quality factor (Qxf). In this paper, a novel low-permittivity borate ceramic (LiBO 2) was synthesized using a conventional solid-state reaction method. Based on the X-ray diffraction and Rietveld refinement, the LiBO 2 crystallized into a monoclinic structure with a space group of P21/c. Dense and single-phase ceramic was obtained at 640 °C with comprehensive microwave dielectric properties: a low relative permittivity (ε r) of 5.3, a moderate quality factor (Q × f) of 18,200 GHz at 16.3 GHz, and a temperature coefficient of resonant frequency (τ f) of − 66.2 ppm/°C. Good chemical compatibility with Ag electrode and thermal expansion coefficient of 25.4 ppm/°C was achieved demonstrating the potential applications as dielectric resonances in wireless communications and substrates in low-temperature cofired ceramics. [ABSTRACT FROM AUTHOR]