Structural evolution and microwave dielectric properties of (1 − x)Sr₂TiSi₂O₈ – xTiO₂ composites for C-band dielectric resonator antennas

Abstract This study investigated the effect of adding TiO 2 (5, 10, and 15%) on the structural and dielectric properties of Sr 2 TiSi 2 O 8 (STS) ceramics in the microwave region. STS exhibits promising microwave dielectric properties (ε’ r = 12.7, tan δ = 1.3 × 10 − 2 and τ f = -22.98 ppm·°C − 1 ), while TiO 2 was selected because of its high permittivity (ε’ r > 85), low dielectric loss on the order of 10 − 4 , and positive above + 400 ppm·°C − 1 which are complementary to the negative τ f of STS. The STS and the composites were produced via solid-state reaction. X-ray diffraction combined with Rietveld refinement revealed the formation of secondary phases (SrTiO 3 and SiO 2 ). Scanning electron microscopy showed significant changes in grain morphology with increasing TiO 2 content, and these changes are reflected in the dielectric properties obtained using the Hakki–Coleman method. Consequently, the TiO 2 additions led to an increase in dielectric permittivity from 10.00 to 24.02, a reduction in loss tangent from 1.74 × 10 − 2 to 3.3 × 10 − 3 , and an increase in the quality factor from 464.75 to 1685.18 GHz. The performance of the materials as Dielectric Resonator Antennas (DRAs) was evaluated both experimentally and through numerical simulation using HFSS software, showing good agreement between the results. The STS15 sample exhibited the best electromagnetic performance, with reflection coefficient S 11 = − 53.75 dB, high radiation efficiency (96.26%), and operation in the C-band. The results demonstrate that the modifications induced by TiO 2 addition control the structural and microstructural evolution of the STS matrix, directly influencing the dielectric properties and electromagnetic performance of the DRAs. This highlights the potential of these composites for applications in C-band microwave communication systems.