Design of Novel Microstrip Bandpass Filters with Cross-coupled Resonators and DGS/Slow-wave Structures

• Main Authors: Chi-Cheng Huang, 黃繼徵
• Other Authors: Ching-Her Lee
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/99034233572552652407

碩士 === 國立彰化師範大學 === 電子工程學系 === 93 === In this thesis, we first propose a novel microstrip BPF designed using triangular open-loop resonators and DGSes of folded-line shape. By appropriately choosing the tapping positions of the resonator feed-lines, the created transmission zeros can be properly located to improve the skirt rejection. Also, with the addition of the newly designed folded-line DGS, the skirt rejection at the upper passband edge can be increased. Results demonstrated that such a filter design can achieve a compact circuit size and a sharp passband skirt while retaining the insertion loss at a relatively low level. Next, a newly designed cross-coupled microstrip BPF with interdigital resonators is investigated. The interdigital structure provides a larger capacitance for the resonator, and hence causes the resonance to move to a lower frequency. The proposed BPF has three transmission zeros; two of them are attributed to the cross-coupled configuration; another one is created by the capacitively-loaded (which is realized by open stubs at the microstrip line end) coupled lines. The former two transmission zeros are located at the lower and upper passband edges to increase the passband rejection, while the latter one is positioned at a higher frequency to suppress the second harmonic. Finally, we present a new slow-wave microstrip BPF with H-shape resonator loads. By making use of the parallel and series resonance characteristics of the H-shape resonator, the loaded transmission line filter can operate as a BPF. The influence of the feed-line tapping position to the load and the feed-line length is examined. A technique which employs an additional H-shape resonator to produce a transmission zero at a higher frequency for second-order harmonic suppression is also presented. Compared with the BPFs constructed using coupled resonators, the newly designed slow-wave BPF shows relatively lower insertion loss and higher selectivity. The work completed in this thesis covers many attractive filter geometries that can be practically applied in real microwave BPFs. The techniques developed in this research are expected to serve as a useful reference for new microwave filter design.