Improved sinterability and temperature stability in Zn2+/Ti4+-co-substituted CaAl2O4 ceramics and their 5G antenna applications

CaAl2 − 2xZnxTixO4 (x = 0.05, 0.10, 0.15) ceramics with low permittivity have been prepared via a standard solid-state reaction method. The partial co-substitution of (Zn0.5Ti0.5)3+ for Al3+ can effectively lower the sintering temperature of CaAl2O4 ceramics by approximately 200 °C. Meanwhile, the large negative temperature coefficient of resonant frequency (τf = − 55 ppm/°C) of CaAl2O4 ceramics can be simultaneously modified toward zero. With increasing x, the quality factor (Qf) indicates a downward changing trend owing to the appearance of ZnAl2O4 and CaTiO3 secondary phases. The optimum microwave dielectric properties (er = 11.9, Qf = 28,090 GHz, and τf = − 1.2 ppm/°C) are achieved at x = 0.15. Moreover, a microstrip patch antenna is fabricated using the x = 0.15 ceramic as the dielectric substrate. The fabricated antenna demonstrates a S11 value of − 17.8 dB at 4.9 GHz and a measured − 10 dB bandwidth of 86 MHz. The good antenna performances suggest that the present ceramics are good candidates for 5G antenna applications at the sub-6 GHz band.