| 摘要: | 本論文以改善吸收式帶止濾波器通帶響應為目標，分為改善低頻通帶植入損耗及高頻通帶頻寬兩部份，且低頻通帶植入損耗版本提出兩種通帶改善方式。
首先，以印刷電路板來實現低頻通帶響應改善電路，止帶中心頻率均為2 GHz，分別使用四分之一波長開路殘段及步階阻抗轉換器兩種方式來改善通帶響應，且改善後仍維持良好的止帶吸收效果。使用開路殘段來改善通帶後，植入損耗小於0.5 dB之通帶頻寬由dc到0.4 GHz增加為dc到0.5 GHz。而使用步階阻抗轉換器來改善，則可依規定要求自訂須改善的頻率，其中通帶中心頻率為1 GHz的設計，植入損耗從0.92 dB改善為0.36 dB；通帶中心頻率為0.67 GHz的設計，植入損耗從0.64 dB改善為0.21 dB。以橋式T線圈取代傳輸線，實作單頻、雙頻及三頻吸收式帶止濾波器通帶響應改善版本，且達到微小化目的，並實作於積體被動元件(IPD)製程。單頻設計方面，與改善前相比，使用開路殘段進行改善後，通帶植入損耗小於1.3 dB從dc到0.32 GHz增加為dc到2.25 GHz。若使用步階阻抗轉換器來改善，單頻版本。通帶中心頻率2.4 GHz的植入損耗從1.1 dB改善到0.66dB；雙頻版本。通帶中心頻率2.4 GHz的植入損耗從1.88 dB改善到0.83dB；三頻版本。通帶中心頻率2.4 GHz的植入損耗從3.43 dB改善到1.4 dB。由以上可知使用此兩種方法皆可達到很好的通帶改善效果，且電路面積亦可大幅縮減。
而高頻通帶頻寬改善則使用雙頻橋式T線圈來達到通帶頻寬增加的效果。使用開路殘段來實現的帶止濾波器原本高低止帶頻率比只有3:1，改善後則可達到4:1，有達到增加頻寬的目的，且電路面積亦由於使用橋式T線圈而能大幅減小。
;In this thesis, improving the passband performance of an absorptive bandstop filter (ABSF)is the target of this research. Two cases are considered. One is the insertion loss improvement of the lower passband, and the other is the bandwidth improvement of the upper passband. In addition, two different methods are proposed for improving the insertion loss of the lower passband.
First, design examples of single-band ABSF with lower passband insertion loss are realized on PCB. The stopband center frequency is 2 GHz. Additional open stub or stepped impedance inverter is used to improve the passband insertion loss while maintaining good stopband rejection. Specifically, by introducing an open stub to the conventional ABSF, one can improve the 0.5-dB insertion loss bandwidth of passband from dc-0.4 GHz to dc-0.5 GHz.. On the other hand, by using a stepped impedance inverter, one can reduce the insertion loss of passband with arbitrarily specified passband center frequencies. Two design examples are presented to validate the proposed design theory. For case A, the passband center frequency is 1 GHz and the insertion loss is improved from 0.92 dB to 0.36 dB. For case B, the passband center frequency is 0.67 GHz while the insertion loss is improved from 0.64 dB to 0.21 dB. Next, bridged-T coils are employed to replace the transmission line sections in the original designs so as to reduce the circuit area and achieve multi-band ABSF designs with lower passband insertion loss. Several design examples are realized in GaAs, WIPD and IPD process technologies to validate the proposed design method. Miniaturized single, dual, and triple band ABSFs with passband improvement are proposed. Compared with conventional designs, proposed single-band ABSF employing the open stub features a 1.3-dB insertion loss bandwidth from dc to 2.25 GHz, while that of the conventional design is from dc to 0.32 GHz. In addition, the proposed design with a stepped impedance inverter also features much better passband insertion loss as compared with the conventional designs. For the proposed single-band ABSF, the insertion loss at the passband center frequency of 2.4 GHz is improved from 1.1 dB to 0.66dB. For the proposed dual-band ABSF, the passband insertion loss at 2.4 GHz is improved from 1.88 dB to 0.83dB. For the proposed triple-band ABSF, the passband insertion loss at 2.4 GHz is improved from 3.43 dB to 1.4 dB. All of these circuits mentioned above have a better response in passband and a very compact circuit size.
Finally, ABSF with a wider upper passband bandwidth is proposed by increasing the frequency ratio of the spurious and of the fundamental stopband. The frequency ratio of the conventional ABSF design is 3:1, while the proposed design employing bridged-T coils features a frequency ratio of 4:1. In addition, the circuit area is also much reduced by using bridged-T coils for the ABSF design. |
