Resonant-Mode Characteristics of a New Three-Mode Hybrid Microstrip/Slotline Resonator and Novel Realization of Compact Bandpass Filter with Four Transmission Zeros

Masataka OHIRA
Zhewang MA

IEICE TRANSACTIONS on Electronics   Vol.E95-C    No.7    pp.1203-1210
Publication Date: 2012/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.1203
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Trends of Microwave Systems and Their Fundamental Technologies)
bandpass filter,  microstrip line,  slotline,  transmission zeros,  three-mode resonators,  source/load coupling,  

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This paper proposes a new three-mode resonator, which consists of a parallel-coupled microstrip line resonator embedded with a slotline resonator, and develops a compact low-loss bandpass filter (BPF) with a sharp roll-off response because of four transmission zeros (TZ) located very near the passband. Resonance mechanism and properties of the three modes are first analyzed by using an eigen-mode analysis, and then an equivalent circuit model is established for expressing a novel coupling scheme of the developed BPF. It is made clear from the results of circuit analysis that the four TZs are produced because of multiple paths between the input/output stub lines formed by the three resonant modes and the direct source/load coupling. The validity of the proposed resonator and filter is supported by the comparison between simulated and measured results.