Ding Shihua

Tapped Multilayer Bandpass Filter on Bi-Based Ceramics

Based on ceramic lamination, a multilayer microwave bandpass filter was fabricated with high dielectric constant (> 80), low temperature co-fired (∼950°C) Bi-based dielectric ceramics. Green ceramic sheets were manufactured by tape casting process and a gold conductive paste was used as the inner electrode. The filter is composed of two coupled stepped-impedance stripline resonators and the input/output ports of the filter are implemented with transmission lines directly tapped to resonators. Since the tapped lines and stepped-impedance resonators (SIRs) were arranged in the same layer, it makes the structure of filter simpler and needs fewer layers than the conventional input/output coupling structure. The admittance matrix for equivalent circuit of the tapped filter was obtained from the four-port coupled-line parameter matrix. The filter with tapped resonators was designed at center frequency at 1.8 GHz. The dimensions of the experimental filter are 4.5 mm × 3.2 mm × 1 mm.

Microwave Dielectric Properties of Bi1-xLixNbO4 Ceramics

With Li2CO3 as an additive, the densified Bi1−x Li x NbO4 (x = 0.0004, 0.0006, 0.0008 and 0.001) ceramics were obtained after sintering at 950°C for 3 h. The structure and microwave dielectric properties were studied. Dielectric constants are 38.09, 38.57, 38.57 and 38.62, Q values are 3001, 1534, 1508 and 1401 and TCF values are 15.6, 8.4, 16.1 and 13.8 ppm/°C for x = 0.0004, 0.0006, 0.0008 and 0.001 respectively at room temperature. The dependence of the Q value and dielectric constant of Bi1−x Li x NbO4 ceramics on temperature at 5 GHz showed that the Q value increased with the increase of temperature and then decreased, the dielectric constant slightly decreased with the increase of temperature and then increased. The defect structure of the Bi1−x Li x NbO4 ceramics was proposed.

Microwave Dielectric Properties of Bi1-xCexNbO4 Ceramics

The microstructure and microwave dielectric properties of Bi1−x Ce x NbO4 (x = 0.01, 0.03, 0.05 and 0.1) ceramics with CuO-V 2 O 5 mixture as a sintering aid have been investigated. The phase transition (from orthorhombic to triclinic phase) temperature of Bi1−x Ce x NbO4 ceramics was lower than BiNbO4 (1020°C). The variation of dielectric constants, Q values and temperature coefficient of resonator frequency (TCF) values with Ce content were examined, so did the variation of dielectric constants with temperature. Bi0.97Ce0.03NbO4 ceramic, sintering at 890°C, exhibits the microwave dielectric constant 41.58, the maximum quality factor (Q) value 5000 (at 5.4 GHz) and TCF value −4.9 ppm/°C.