雙模可切換濾波器

Abstract

本論文提出一個中心頻率為2.5GHz的雙模可切換濾波器。此電路為對稱的結構，利用二極體順向偏壓及逆向偏壓的切換來改變濾波器的特性，使得在二極體順向偏壓時只有共模信號可通過電路而奇模信號則會被阻絕，在二極體逆向偏壓時則反之。 本論文的研製主要由帶通濾波器的設計開始，並將二極體及電容的特性參數帶入，設計出等效的半電路，其次進行帶止濾波器及全止濾波器的分析，接著將這些等效的半電路轉換為對稱結構的電路，即可取得此雙模可切換濾波器的架構。此論文中電路的工作頻帶為2.4GHz~2.6GHz，並且以微帶線製作在介電常數3.58、厚度為20mil的RO4003的基板上。

A switching circuit of the center 2.5GHz is proposed in this thesis. The circuit is symmetrical, and it may pass the odd mode signal and reject the even signal or vice versa. As the diodes are turned (forward bias), the even mode can pass through the circuit and the odd mode will be rejected. On the other hand, as the diodes turned off (reverse bias), the situation reversed. Firstly, we design the band-pass filter and take the characteristic of the components into consideration, and then we may analyze the performance of the band-stop filter and the all-stop filter. Combining these half circuits (2 band-pass filters, 1 band-stop filter, 1 all-stop filter), we may get the whole structure of the switching circuit. The whole circuit in this thesis is operated in 2.4GHz~2.6GHz. It is fabricated with microstrip line on a RO4003 substrate with a dielectric constant of 3.58, a thickness of 20 mil.