減衰極を有するUWBバンドパスフィルタの理論設計

摘要

A quasi-elliptical-function-based design methodology is proposed for ultra-wideband(UWB) filters consisting of stepped-impedance resonators (SIRs) based on parallel-coupled three-line, short-circuited stubs and two-section steppea-impedance open-ended stubs. Firstly, UWB filters composed of merely SIRs and short-circuited stubs are synthesized in terms of a transmission-line-theory-based chebyshev-filter-synthesis technique. Then, two-section open-circuited stubs are theoretically designed to replace the short-circuited ones. Accordingly, a pair of controllable attenuation poles is introduced to significantly improve the selectivity of the filter. Furthermore, the influence of the location of the loaded stubs to the filter characteristics is investigated to show that good out-band characteristics are obtained when the open-ended-stubs are loaded at input/-output-ports, whereas the load of the stubs in SIR brings in spurious near the introduced transmission zeros. Theoretical simulation also shows that the filter with a short-circuited stub and an open-circuited stub exhibits better out-band characteristics than that with two open-circuited stubs. As an example, a UWB BPF with a fractional bandwidth (FBW) of 110% (BW: 3.1～10.6GHz) is then synthesized, simulated, fabricated and measured. The measured frequency responses of the UWB filter compare very well with the predicted ones and successfully satisfy outdoor specifications of FCC, which validates the correctness and effectiveness of the proposed technique.%伝送線路理論に基いて，平行結合三線路に基いたステップインピーダンス共振器(SIR)と先端短絡，先端開放スタブを組み合わせた超広帯域(UWB)フィルタの設計理論を提案した.先ず，SIRと先端短絡スタブを組み合わせたチェビシェフ型フィルタを合成理論に基いて設計する.次に，伝送線路理論に基づいて，先端短絡スタブを先端開放スタブに置き換えることにョり，減衰極を有するフィルタを実現する.更に，スタブの接続場所の周波数特性への影響について検討した.スタブがフィルタの入出力端に付加される場合，設計したフィルタが良い帯域外特性を示すが，スタブがSIR部分に付加される場合，阻止帯域にぉレヽてスプリァスが生じるため，提案した手法が使用不可能になることが分かる.次にスタブの組み合わせ方の帯域外特性への影響について検討し，2つの先端開放スタブを用いるョり，先端短絡スタブと先端開放スタブを1つずつ使った方が，フィルタの帯域外特性がョり良いことを示した.実際例として，提案した設計理論を用いて，FCCの屋外仕様を満たす3.1-10.6GHz(FBW:110%)の帯域を持つ小型(13.05mm)超広帯域バンドパスフィルタを設計し，実際に作製し，測定した.シミュレーション結果と測定結果はョく一致していることにョり，提案した設計理論の妥当性及び有効性が確認された.