Low sintering temperature high permittivity glass ceramic composites for dielectric loaded microwave antennas

Abstract

Abstract

Due Owing to the presence of metallizations on their surface, the property requirements for dielectric loaded antennas (DLAs; quality factor Qf₀ of >5000 GHz and temperature coefficient of resonant frequency of −40<τ_f<+40 MK⁻¹) are less stringent than for cavity filters (Qf₀ of >30 000 GHz, τ_f = ±1 MK⁻¹ and relative permittivity of 20<ϵ_r<50). ϵ_r, however, should be as high as possible to decrease the component size and raw materials, and the energy production costs must be minimised since the DLAs are incorporated into the mobile handsets. In the present work, the use of in-house glass (BN1, 30Bi₂O₃–30Nb₂O₅–30B₂O₃–10SiO₂, mol.-%) as an aid to reduce the sintering temperature of barium neodymium titanate (BNT, Ba₄Nd_9·33Ti₁₈O₅₄) ceramics is studied. The addition of 10 wt-% BN1 glass to BNT (BNT-10BN1) resulted in a 150°C decrease in sintering temperature of BNT. However, the glass reacted with the BNT ceramic and formed an unknown pyrochlore structured phase, which resulted in a decrease in ϵ_r from ∼80 to ∼73, Qf₀ from 8400 to 2800 GHz and τ_f from ∼65 to 40 MK⁻¹. ϵ_r, Q and τ_f further decreased when 20 wt-% BN1 glass was added to BNT ceramics. Despite the reduction in material properties, BNT-10BN1 was still considered suitable for DLA applications.

Keywords:

• Microwave materials
• Antennas
• Dielectrics
• Transmission electron microscopy
• Composite

The authors are grateful to Professor D. Sinclair for valuable comments on the impedance spectroscopy data.