微帶線濾波器存在著寄生響應(Spurious Responses) 造成導通帶和截止帶在頻率軸上不斷重複出現。本文探討寄生響應產生的原因、出現的位置以及抑制的方式。本文提出一種具有抑制寄生響應的新型微帶線帶通濾波器，主要是利用兩個非對稱型式的步階阻抗諧振器所構成。藉由在二分之一波長諧振器上，設計不同的阻抗比及長度比，使高階寄生響應會相互抵消，因此濾波器具有寬廣的截止帶。並利用HFSS軟體分析比較對稱型式及非對稱型式的濾波器，證明非對稱型式的濾波器具有較寬的截止帶，此外模擬分析零度和180度饋入，發現使用零度饋入技術可在截止帶兩側插入零點並保持相同的導通帶響應與寄生響應抑制範圍不變。
在實作方面，分別將濾波器實現在FR4、氧化鋁與BaZn2Ti4O11 (BZT)等三種基板上，所設計的濾波器中心頻率為1.5 GHz、頻寬為8%、Shape Factor小於2、截止帶頻率為基本諧振頻率的5倍以上。並另外將此濾波器設計在2.4GHZ下，中心頻率為2.4 GHz、頻寬為10%。模擬和量測結果顯示，濾波器頻率、頻寬都與模擬非常相近。1.5 GHz的濾波器在抑制寄生響應方面FR4基板上可被抑制到5.41f0、Al2O3基板上可被抑制到5.09f0、BZT基板上可被抑制到4.55f0處。另外，2.4 GHz的濾波器在FR4基板上寄生響應可被抑制到4.58f0，略小於1.5GHZ時的範圍。但上述的濾波器其Shape Factor皆大於2。

In general, the microstrip bandpass filters (BPF) suffer the problems of spurious responses in which the passbands and stopbands appear alternatively in the frequency spectrum. Suppressing the spurious responses effectively will remove the necessity of extra low-pass filters in front of or behind the bandpass filters. In this thesis we investigated the causes of the spurious responses and proposed a modified microstrip bandpass filter to enhance the capability of spurious responses suppression by using asymmetric stepped-impedance resonators. By choosing the proper stepped-impedance ratio and length ratio for the stepped-impedance resonators, the spurious responses beyond the desired passband can be suppressed effectively, resulting in the BPF with broad stopband. The HFSS simulation was first used to analyze the BPFs with symmetric and asymmetric stepped-impedance ratios and length ratios. The results showed that the stopband of asymmetric filters is wider that that of symmetric filters. The simulation also demonstrated that the spurious response suppression was almost the same for both zero degree and 180 degree signal feeds. The BPFs with spurious response suppression were realized on FR4, Al2O3 and BaZn2Ti4O11(BZT) substrates, respectively. The BPFs were designed with the characteristics of the center frequencies of 1.5 and 2.4 GHz, 8% bandwidth and the stopband with the suppression frequency five times over the center frequency. The measured results of the BPFs agreed with the simulations. However, the measured loss was larger than that of simulation due to fabrication errors. The shape factor of the filters was larger than two, which is a little bit over the accepted value for practical industry bandpass filters and needs further improvement in the future.

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