An Effective Method for Designing Bandpass Filters Using λ/4 Resonators for Improving Out-of-Band Characteristics

Kouji WADA  Tomohide KAMIYAMA  Osamu HASHIMOTO  

IEICE TRANSACTIONS on Electronics   Vol.E86-C   No.2   pp.150-161
Publication Date: 2003/02/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Circuit and Device Technology for High-Speed Wireless Communication)
Category: Passive (Filter)
λ/4 resonator,  attenuation pole,  skirt characteristics,  spurious responses,  bandpass filter,  

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A design methodology of bandpass filters (BPFs) using λ/4 resonators for improving out-of-band characteristics is proposed. Firstly, the basic characteristics of various λ/4 resonators are examined. In this study, we focus on four types of λ/4 resonators, i.e., (1) direct-coupled λ/4 resonator, (2) loaded-element λ/4 resonator, (3) tapped λ/4 resonator and (4) loaded-element tapped λ/4 resonator. Secondly, the application examples of BPFs with improved out-of-band characteristics are provided. We examine the improvement of filter characteristics, i.e., sharp skirt characteristics and low spurious responses. The results of this study lead us to the conclusion that the methodology is very useful for improving the out-of-band characteristics of the BPFs using the λ/4 resonators.