Compact coaxial dielectric bandpass filter with load-source coupling

Second-order coaxial dielectric ceramics filters with one or two transmission zeros (TZs) have been presented. The TZs are analyzed in detail. The results showed that source and load can be regarded as virtual resonators, two resonators of a second-order filter together with virtual resonators can form a four-resonator known as the CQ, one resonator of the filter together with virtual resonators forms three section resonator known as CT. A chip capacitor (0.5PF) is used as a cross-coupling elements. Second-order filters, made of monoblock ceramics with dielectric constant of 75, were been fabricated and measured, which produced two TZs both above and below passband, one TZs above or below passband, respectively. The sizes of the fabricated filters are 14mm×6.5mm×8mm (0.045λ₀×0.02λ₀×0.026λ₀). The measured results agreed well with the design.