Out-of-Band Improvement by Microstrip Line BPFs with Multiple Attenuation Poles in Stopband Using Various Conditions of Coupling Length of Partially Coupled-Line Section

Kouji WADA  Ramesh K. POKHAREL  Takanobu OHNO  Osamu HASHIMOTO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E88-C   No.7   pp.1430-1439
Publication Date: 2005/07/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.7.1430
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Technologies of Microwave and Millimeter-Wave Devices Focusing on Miniaturization and Advancement in Performance with Their Applications)
Category: Resonators & Filters
Keyword: 
coupled-line BPF,  attenuation poles,  out-of-band characteristics,  spurious responses,  microstrip line,  

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Summary: 
In a partially coupled-line bandpass filter (BPF), a combination of two microstrip line resonators which are partially coupled, are considered, where one resonator is half-wavelength (λ/2)-long, and another whose one end is grounded, is only quarter-wavelength (λ/4)-long. Therefore, the length of a coupled-line section can be varied based on the position of the grounding end, and five conditions of the movable coupling length have been simulated which will greatly influence the spurious responses of a BPF. This property is numerically investigated in this paper. The analysis shows that, based on the grounding position, this method is capable of realizing the improved out-of-band characteristics by locating the multiple attenuation poles in the stopband and improved spurious responses up to five times of the center frequency (5f0). A few empirical models of BPF are fabricated, and the numerical results are ensured by comparing with the experimental results.