New tap-coupling technique for improving skirt characteristics of a λ/4 resonator bandpass filter by placement of attenuation poles

Improvement of the skirt characteristics of a λ/4 resonator bandpass filter (BPF) is carried out by placement of attenuation poles. In this study, the characteristics of the tapped-resonator are effectively used because the attenuation pole can easily be realized, and the external Q of the resonator can be controlled. However, the technique includes the limitation of flexibility for the placement control of the attenuation pole. Therefore, we try to improve flexibility for placement control of the attenuation pole under the characteristics of the lumped-element loaded stub. It has been clarified that the proposed technique is useful for improving the skirt characteristics of the λ/4 resonator BPF.