Development of Patch Antenna Substrate in BaO-4.TiO₂ System

Abstract

BaTi4O9(BT4), has dielectric constant (εr)≈36 and unloaded Q-factor (Qf) >35,000GHz, but has temperature coefficient of frequency (τf~16-20ppm/°C). Ba2Ti9O20(B2T9), very near to BT4 in the BaO-TiO2phase diagram, has εr~38, Qf~35,000GHz and τf<4ppm/°C. Though this phase is selected for most of the applications, there are many challenges like slow formation, decomposition, reaction with substrate etc. But, BT4 formed quickly and densified easily, but only high τf precluded it from many practical applications. Most of the literature on the modification of BT4 decreased the εr≤35. Here, the preparation and properties of ZnO/ZnTiO3added BaTi4O9ceramics are reported. The ceramics have been prepared by the solid state method. Raw materials have been homogenized and calcined at 1125°C. Calcined powders are ball-milled, compacted and sintered in 1275−1350°C to get dense ceramics with ρ=4.38-4.44 g/cc (TD>97.5%). XRD analysis has confirmed the BaTi4O9phase formation along with secondary phases. FeSEM microstructures show liquid phase assisted sintering leading to fused grains and exaggerated grain growth. The dielectric properties have been measured near 4GHz by standard rod resonator methods using cylindrical specimens. The ceramics have εr36.5−38, τf<11ppm/°C and Qf>17THz. It is possible to further improve the Qf of these ceramics by controlling the processing.