Ultra-Wideband Bandpass Filter with Sharp Attenuation Slope Using Inter-Digital Finger Resonator and Parallel-Coupled Lines

Takenori YASUZUMI  Yusuke OMOTE  Tomoki UWANO  Osamu HASHIMOTO  

IEICE TRANSACTIONS on Electronics   Vol.E95-C    No.2    pp.268-274
Publication Date: 2012/02/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.268
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electronic Circuits
bandpass filter (BPF),  ultra-wideband (UWB),  inter-digital finger resonator,  parallel-coupled lines,  microstrip line (MSL),  

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This paper presents an ultra-wideband (UWB) bandpass filter (BPF) with sharp attenuation slope characteristics. The circuit structure consists of an inter-digital finger resonator, parallel-coupled lines and phase matching line. The design of the bandwidth was described by using the even and odd mode characteristic impedances in the resonator structure. The parallel-coupled lines were also designed in the same manner. The parameters of the resonator and two parallel-coupled lines in combination as the BPF were then optimized by the simulation with HFSS. The designed BPF was experimentally fabricated and its measured performances showed the bandwidth from 3.6 to 10 GHz with the 20 dB outband rejection. For the U.S. UWB band design, the matching line was inserted between the two parallel-coupled lines. The matching at both band edges was then qualitatively analyzed on the smithchart. The HFSS simulation results of the structure realized the bandwidth from 3.1 to 10.6 GHz with sharp attenuation slope characteristics for SWR < 2.0. The measurement results agree well with the simulation results.