具多重選擇性頻帶配置之四頻段濾波器設計

Abstract

本篇論文主要著重於不同類型頻帶配置之四頻段帶通濾波器，並提出兩種設計方法。兩種設計方法皆實現於印刷電路板上，並經過實驗的驗證。 第一種類型是針對四個頻段皆相當靠近的配置，其想法是將單頻段的濾波器經由轉換公式，把單頻的極點和零點根據各個頻段的截止頻率點去轉換組合出多頻段的極點和零點；藉由這些極點和零點可以合成該響應所對應的耦合矩陣元素值；接著我們也對n階的響應做理論分析與預測，並探討極點與零點的分布數目；最後，為了減少諧振器的使用數目，提出了多模態與單模態諧振器之間諧振頻率點之萃取方法；一旦有關諧振頻率點所組成的小模組被建立，即可從基本單頻段柴比雪夫響應直接實現出多頻段之帶通響應，以達到快速與低成本的電路設計。 第二種類型則是可任意決定頻帶位置的四個頻段之設計。其想法是利用頻率的正交性將四個單頻段通帶並接成一個四頻段的響應，再透過平行耦合線共用的方式，作為濾波器的輸入輸出級，使其同時符合四個頻段之外部品質因子，如此可避免由饋入線所造成的負載效應。此外，引入多模態諧振器來取代數個單模態諧振器的概念，並以耦合矩陣的概念說明模態頻率落點位置，可大幅減少諧振器數目與電路面積，最後則針對止帶做改善。 本論文共實作了三個電路，模擬與量測結果一致。有關第一種類型，分別使用半波長開路諧振器與網狀諧振器來實現，電路面積各為 1.18λg × 0.144λg 與 0.533λg × 0.27λg ，中心頻1.86、1.95、2.04、2.14GHz與1.82、1.94、2.06、2.18GHz，比例頻寬1.5%、1.33%、1.33%、1.5%與2.2%、1.85%、1.75%、1.84%，介入損耗則為2.2、2.3、1.8、1.3dB與1.2、1.7、2、1.2dB。至於第二種類型則是耦合線與網狀諧振器的組合，電路面積0.788λg × 0.066λg ，中心頻0.8、1.0、1.4、1.8GHz，比例頻寬12.1%、8.3%、5.5%、3.8%，介入損耗則為1.6、2、2.4、2.8dB。

With different requirements on the band allocations, this thesis proposes two methods for the design of quad-band bandpass filters. Thus the designed filters are fabricated on the printed circuited boards and verified by experiments. The first part focuses on the design for closely spaced pass-bands. Through a general idea of frequency transformation, the poles and zeros of a single band response are transformed into poles and zeros of a multiband response according to the cutoff frequency of each band. Then, theoretical analysis is made to predict the nth order response and discuss the distribution of the numbers of poles and zeros. Finally, to reduce the number of resonators, a method for extracting the resonant frequency points between multi-mode and single mode resonators is proposed. If the module about resonant frequency points is constructed, the band-pass response of multi-band could be directly realized by designing the fundamental single-band Chebyshev response and achieving the fast and low-cost circuit design. The second part deals with the case of arbitrarily spaced pass-bands. The design concept is to connect four pass-bands together to form quad-band response by exploiting the frequency orthogonality. Then, to avoid loading effect by tapped line, parallel coupled lines are served as the I/O coupling structure to meet external quality factors for quad-band requirements. Moreover, multi-mode resonators are introduced to replace with many single-mode resonators and utilize the concepts of coupling matrix to explain the location of mode-frequency. By this way, the number of resonators and circuit area can be reduced. Finally, we make improvement for stopband. The four circuits are fabricated in this thesis, and the simulated results show a good agreement with the measured results. About the first part, the open-loop and net-type resonators are applied. These two quadband filters are designed and fabricated with the areas 1.18λg × 0.144λg ,0.533λg × 0.27λg , the center frequencies at 1.86、1.95、2.04、2.14GHz, 1.82、1.94、2.06、2.18GHz, the fractional bandwidth 1.5%、1.33%、1.33%、1.5%, 2.2%、1.85%、1.75%、1.84%, and the insertion loss 2.2、2.3、1.8、1.3dB, 1.2、1.7、2、1.2dB, respectively. The second part is the combination of coupled lines and net-type resonators. The occupied area is 0.788λg × 0.066λg , the center frequencies at 0.8、1.0、1.4、1.8GHz, the fractional bandwidth about 12.1%、8.3%、5.5%、3.8%, and the insertion loss 1.6、2、2.5、2.7dB.