Dual-Narrowband/Wideband Filters Using Modified Coaxial Cavities With Large Frequency Ratios

This article presents two types of dual-narrowband/ wideband filters using modified coaxial cavities with large frequency ratios. The dual-narrowband/ wideband filters mean two dual-band bandpass filters, one of which is a dual-band wideband filter, and the other is a dual-band narrowband filter. The proposed coaxial resonator in the dual-narrowband filter consists of a pair of disk-loaded coaxial stepped impedance resonator (DLCSIR), which provides a large frequency ratio. The frequency ratio of the first two resonant modes of the DLCSIR can be precisely controlled by adjusting the impedance ratios and dimensions of the loading disk. By contrast, the proposed coaxial resonator in the dual-wideband filter is a rectangular coaxial stepped impedance resonator (RCSIR), which has the merits of miniaturized size, large frequency ratio, and convenience for strong coupling. Finally, two second-order dual-narrowband/ wideband filters with large frequency ratios were designed, fabricated, and measured. The exhibited dual-passband performance of the two filters verifies the proposed concept.