Synergistic Dual‐Phase and Microstructure Engineering toward Temperature‐Stable, Ultra‐Low Loss Li 2 TiO 3 ‐Based Microwave Dielectric Ceramic

High‐performance microwave dielectric ceramics are the essential materials for next‐generation 6G communication devices. However, simultaneously achieving temperature stability and ultra‐low loss remains a formidable challenge. To address this, a monoclinic‐cubic dual‐phase structure is engineered in Li 2 Ti 0.95 (Ga 1/2 Ta 1/2 ) 0.05 O 3 ceramic through LiF‐triggered dual‐phase formation. This unique structure effectively balances the opposing temperature coefficient of resonance frequency (TCF) between the monoclinic (positive TCF) and cubic (negative TCF) phases, thereby achieving a near‐zero TCF. Furthermore, ultra‐low dielectric loss is attained through the intrinsic suppression of oxygen vacancies via charge‐compensated substitution, coupled with LiF‐assisted liquid‐phase sintering that simultaneously promoted a dense microstructure. Benefiting from the synergistic effect, the optimized Li 2 Ti 0.95 (Ga 1/2 Ta 1/2 ) 0.05 O 3 ‐2 wt.% LiF (LTGT‐2LF) ceramic exhibits superior comprehensive properties, featuring an ultra‐high Q × f value of 126,760 GHz, a near‐zero TCF of +9.7 ppm/°C, and robust mechanical strength (flexural strength = 151.7 MPa). To demonstrate its potential for practical applications, a cylindrical dielectric resonator antenna (CDRA) based on LTGT‐2LF ceramic is designed and fabricated, exhibiting a high gain (4.6‐5.3 dBi) and radiation efficiency (> 80%). This work establishes a viable strategy for designing high‐performance microwave dielectric ceramics by synergistic engineering of phase structure, defect chemistry, and microstructure.