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Miniature Microstrip Bandpass Filters Based on Capacitive Loaded Coupled-Lines and Lumped-Element K-Inverters
Yo-Shen LIN Chien-Chun CHENG
IEICE TRANSACTIONS on Electronics
Publication Date: 2007/12/01
Online ISSN: 1745-1353
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Technologies for Microwave and Millimeter-wave Passive Devices)
bandpass filter, capacitive loaded, cross-coupled, K-inverter, lumped-element, parallel-coupled,
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This study presents a class of miniature parallel-coupled bandpass filters with good selectivity and stopband rejection. Capacitive terminations are introduced to the conventional anti-parallel coupled-lines, and lumped-element K-inverters are employed, to achieve both size reduction and spurious suppression. Additionally, the capacitive cross-coupling effect can be introduced to obtain three transmission zeros to enhance the selectivity. Suitable equivalent-circuit models, along with design formulae, are also established. Specifically, via design examples, this work demonstrates the feasibility of proposed filter structures in microstrip configuration. Compared to the conventional parallel-coupled filters, the proposed filters exhibit over 60% size reduction, improved selectivity, and wider stopbands up to four times the center frequency.