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Dense (1− x)Ca(Mg1/3Ta2/3)O3/ xCaTiO3 ceramics (0.1≤ x≤0.9) were prepared by a solid-state reaction process. The crystal structures and microstructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Single-phase solid solutions were obtained in the entire composition range. Long-range 1:2 ordering of B-site cations and oxygen octahedra tilting lead to the monoclinic symmetry with space group P21/ c for x=0.1. For x above 0.1, the long-range ordering was destroyed and the crystal structure became the orthorhombic with space group Pbnm. The microwave dielectric properties showed a strong dependence on the composition and microstructure. The dielectric constant and temperature coefficient of resonant frequency increased nonlinearly as the CaTiO3 content increased while the Qf values decreased approximately linearly. Good combination of microwave dielectric properties was obtained at x=0.45, where ℇr=45.1, Qf=34 800 GHz, and τf=17.4 ppm/°C. [ABSTRACT FROM AUTHOR]