Effect of TiO₂ doping on dielectric properties and temperature stability of Ca₃(BO₃)₂ microwave ceramics with feasibility simulation for 5G antennas

Low-perittivity (1–x)Ca₃(BO₃)₂–xTiO₂ (CBTO, x = 0–0.25) ceramics were fabricated via cold sintering. Phase composition was confirmed by XRD. The effects of TiO₂ doping on the dielectric properties and temperature stability (τ_f) were systematically investigated. Guided by lattice dynamics, phonon characteristics were probed using Raman and FTIR spectroscopy. Eight Raman-active and ten infrared-active modes were identified. A four-parameter semi-quantum model successfully extracted the intrinsic dielectric parameters, revealing that vibrations related to Ca²⁺ (Mode 4) contributed most significantly (21.89% to ε_r, 32% to loss). TiO₂ addition effectively tuned τ_f from −39.89 × 10⁻⁶ ℃⁻¹ towards zero. This comprehensive phonon analysis established a clear structure–property relationship. The optimal composition (x = 0.20) exhibited a balanced performance: ε_r = 10.56, Q × f = 10,896 GHz, and τ_f = −6.58 × 10⁻⁶ ℃⁻¹. To demonstrate practical utility, a 5G microstrip patch antenna was designed using this ceramic. The antenna resonated at 9.97 GHz with excellent impedance matching (S₁₁ = −49.56 dB) and a peak gain of 6.39 dBi. These results confirm CBTO ceramics as a promising candidate for temperature-stable, high-frequency applications.