A Novel Half-Wavelength Coupled-Resonator Filter with Multiple Attenuation Poles

Recently, miniaturization and high performance of base-station filters are strongly requested. By forming attenuation poles near the passband, attenuation outside the passband can be improved. As a result, the filter can be downsized due to a smaller number of resonators. In this report, a novel half-wavelength coupled-resonator filter is investigated. Although conventional filter makes attenuation poles by cross-coupling, this filter can generate those by using electromagnetic coupling between resonators. The design method for half-wavelength filter is investigated. It is demonstrated how the attenuation pole frequencies varied depending on capacitances connected to the coupled-resonators. In addition, the spurious characteristics are also studied. The second harmonic spurious of half-wavelength resonator can be moved to higher frequency by loading capacitances at both ends of the coupled-line.