Tapped Multilayer Bandpass Filter on Bi-Based Ceramics

Abstract

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.