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

AbstractDue 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<τf<+40 MK−1) are less stringent than for cavity filters (Qf0 of >30 000 GHz, τf = ±1 MK−1 and relative permittivity of 20<ϵr<50). ϵr, 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, Ba4Nd9·33Ti18O54) 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 ϵr from ∼80 to ∼73, Qf0 from 8400 to 2800 GHz and τf from ∼65 to 40 MK−1. ϵr, Q and τf 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.