Novel Dual-Mode Circular Patch Bandpass Filter with Enhanced Stopband Performance

Min-Hung WENG  

IEICE TRANSACTIONS on Electronics   Vol.E88-C   No.9   pp.1872-1879
Publication Date: 2005/09/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.9.1872
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
dual-mode,  patch,  bandpass filter,  perturbation element,  defect ground structure (DGS),  

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This investigation proposed a novel dual-mode circular patch bandpass filter (BPF) with enhanced stopband performance. The novelty of the proposed structure is to use a pair of square etched areas acting as a perturbation element on the circular patch resonator such that two split modes are coupled and the filter structure can be reduced. The coupling coefficients of two split modes are obtained. To improve the stopband performance, a pairs of H-shaped defected ground structure (DGS) cells are used below the input/output port to suppress the spurious response of the proposed BPF. The equivalent circuit of the DGS cell is discussed and the relations between bandstop characteristic and the suitable DGS dimensions are also investigated. The proposed BPF is demonstrated with a central frequency fo = 2.2 GHz, a 3-dB fractional bandwidth of 8% and a wider stopband of -35 dB from 2.5 to 6 GHz. Measured results of experimental filter have good agreement with the theoretical simulated results.