Design of Capacitively Loaded Coupled-Line Bandpass Filters With Compact Size and Spurious Suppression

This paper is focused on the synthesis of capacitively loaded coupled lines for the design of bandpass filters with compact size and spurious suppression. The filters consist of cascaded pairs of coupled lines periodically loaded with patch capacitors. The loading capacitances provide a slow-wave ef...

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Bibliographic Details
Published in:IEEE transactions on microwave theory and techniques 2017-04, Vol.65 (4), p.1235-1248
Main Authors: Orellana, Marco, Selga, Jordi, Velez, Paris, Sans, Marc, Rodriguez, Ana, Bonache, Jordi, Boria, Vicente E., Martin, Ferran
Format: Article
Language:English
Subjects:
Bandpass filters
Capacitors
circuit synthesis
coupled lines
Couplings
electromagnetic bandgap
Filter design (mathematics)
Impedance
Integrated circuit modeling
Loading
microstrip technology
Microwave circuits
Miniaturization
Size reduction
slow-wave transmission lines
space mapping
Topology
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Summary:This paper is focused on the synthesis of capacitively loaded coupled lines for the design of bandpass filters with compact size and spurious suppression. The filters consist of cascaded pairs of coupled lines periodically loaded with patch capacitors. The loading capacitances provide a slow-wave effect to the coupled lines useful for filter miniaturization, whereas periodicity introduces bandgaps that can be controlled in order to achieve spurious suppression. Filter design is achieved following an automated process based on aggressive space mapping (ASM) optimization. The two reported examples, a third-order filter with central frequency f 0 = 1.0 GHz, 8% fractional bandwidth, and 0.1-dB ripple level and a fifth-order filter with central frequency f 0 = 1.8 GHz, 8% fractional bandwidth, and 0.1-dB ripple level, demonstrate the potential of the proposed ASM-based design approach, as well as the effectiveness of the loading capacitances to reduce filter size and reject the spurious bands. Significant size reduction in both filters is achieved, whereas the out-of-band rejection is better than 30 and 45 dB in the third-order and fifth-order filters, respectively, up to at least 4f 0 .
ISSN:0018-9480
1557-9670
DOI:10.1109/TMTT.2016.2638843