利用變容二極體設計可調式髮夾帶通濾波器

Abstract

本論文提出兩種可調式髮夾帯通濾波器的架構與設計方法，一是中心頻率可調式，另一則是頻寬與中心頻率均可調式，皆是利用變容二極體設計，並呈現數個具體電路的模擬、實作的情況與結果的比較。 中心頻率可調式髮夾帶通濾波器採用三階的柴比雪夫響應，利用導納或阻抗轉換器與耦合微帶線之等效，並於髮夾形共振器之微帶線開路端加載變容二極體，藉由調整變容二極體之逆偏壓以達到中心頻率可調之目的。 頻寬與中心頻率均可調式髮夾帯通濾波器採用二階的柴比雪夫響應，使用耦合係數法設計，同樣於髮夾形共振器之微帶線開路端加載變容二極體，藉由調整變容二極體之逆偏壓以達到中心頻率可調之目的。另外，於兩個共振腔之間以及微帶線饋入與饋出共振腔之處各加上一變容二極體，藉由調整變容二極體之逆偏壓而改變耦合量，以達到頻寬可調之目的。 此兩種濾波器的可調頻率範圍設計在1.7 GHz～2.7 GHz，為LTE大部分頻帯落在的區間。可調元件選用M/A com MAVR-000250-12790T (Package: SC-79)與Metelics MGV 125-20 (Package: E28/28X)兩種變容二極體。電路使用型號為Rogers RO4003C、板厚為20 mil、銅厚為0.7 mil、介電常數為3.55、耗損正切為0.0027的板材實作。使用3.5 mm的SMA接頭與型號為Agilent E8364B PNA的網路分析儀作量測。

The thesis introduces the design methods and the structures of the two types of tunable hairpin bandpass filters using varactor diodes. One is the filter with center-frequency tunable, and the other one is the filter with both bandwidth and center-frequency tunable. Several example circuits are realized and the comparisons between simulated and measured results are given. The center frequency tunable filters are the third order Chebyshev response where the equivalence between J/K inverters and microstrip coupled lines are applied. The varactor diodes at the open end of hairpin resonators tune the center-frequency of the resonator with respect to the reverse bias voltages of varactor diodes. The filter with both center frequency and bandwidth tunable is based on the second order Chebyshev response where the coupling coefficient method is adopted for the circuit design. Similar frequency tuning mechanism is adopted. Moreover, cascading a varactor diode between two adjacent resonators and varactor diode between I/O ports and the first/last resonator makes the bandwidth tunable.

The designed tunable range of these two types of filters is from 1.7 GHz to 2.7 GHz which covers most of LTE bands. M/A com MAVR-000250-12790T (Package: SC-79) and Metelics MGV 125-20(Package: E28/28X) varactor diodes are employed to provide tunability. The circuits are fabricated on Rogers RO4003C substrate with thickness of 20 mil, conductor thickness of 0.7 mil, dielectric constant of 3.55, dielectric loss tangent of 0.0027, and connected to 3.5 mm SMA connectors, and measured by Agilent E8364B PNA Network Analyzer.