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Abstract: The crystal structures, phase compositions and the microwave dielectric properties of the (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 perovskite-based composites have been investigated. The (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 solid solutions exhibited an 1:2 ordered monoclinic structure for all compositions. As (Ca0.8Sr0.2)TiO3 content increases, the ɛ r and τ f values increase gradually, while the Q × f values decreases. By appropriately adjusting the x value in the (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 ceramic system, a near-zero τ f value can be achieved. The optimal microwave dielectric properties with a dielectric constant (ɛ r ) value of 43.37, a Q × f value of 46,000GHz (where f =6.8GHz, is the resonant frequency), and a temperature coefficient of resonant frequency (τ f ) of −2.7ppm/°C can be obtained for specimen using (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 (x =0.4) sintered at 1425°C for 3h. It is proposed as a high-dielectric-constant, low-loss dielectric and in particular, a suitable candidate material for today''s 3G passive components and small-sized GPS patch antennas. [Copyright &y& Elsevier]