A Dual-Band Ring-Resonator Bandpass Filter Based on Two Pairs of Degenerate Modes

作者：Luo Sha^*; Zhu Lei; Sun Sheng

来源：IEEE Transactions on Microwave Theory and Techniques, 2010, 58(12): 3427-3432.

DOI：10.1109/TMTT.2010.2053590

• Bandpass filter
• dual band
• dual mode
• open-circuited stubs
• ring resonator
• transmission zeros

In this paper, a class of dual-band ring-resonator bandpass filters is proposed based on a single ring resonator. As its most distinctive feature, two pairs of first-and second-order degenerate resonant modes in a ring resonator are simultaneously excited, resulting in a compact dual-mode dual-band bandpass filter with two transmission poles in both passbands. Firstly, two capacitors or parallel-coupled lines are placed at two nonorthogonally excited positions along a ring resonator in order to excite the two first-order degenerate modes and create multiple transmission zeros. Next, a set of perturbations is introduced on the ring to excite the two second-order degenerate modes. In our design, two excitation positions are first placed with between 45 degrees - and 135 degrees-separation on a ring. Simulations show that, with a proper arrangement of the excitation angle, two transmission poles in the first passband can be excited and more transmission zeros can be generated. Four and eight open-circuited stubs are loaded symmetrically along the ring, resulting in synchronous excitation of two poles in the second passband. Of the two designed filters with 135 degrees- and 45 degrees-separation, the one with 45 degrees exhibits much better out-of-band performance with three additional transmission zeros at frequencies lower than the first passband, between the two passbands and higher than the second passband. Finally, two filter prototypes are fabricated and their measured results are found to be in good agreement with theory.

• 出版日期2010-12
• 单位南阳理工学院