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Compact high selectivity and wide stopband bandpass filter using dual-layer structure

In this paper, a compact bandpass filter with high selectivity and wide stopband using the dual-layer structure is proposed. Fundamental-resonance with two close transmission zeros can be employed and adjusted by the hybrid microstrip/coupled-meander-shape defected ground structure (CMSDGS) cell. Then, based on these cells, an interdigital-coupled scheme with short-stubs is introduced to provide strong narrowband coupling and high selectivity for passband enhancement and stopband spurious suppression, respectively. Therefore, a filter with good passband and stopband responses can be easily achieved. The measured results show that the proposed filter operated at 2.45 GHz (i.e., f0) has the merits of an strong selectivity (i.e., the attenuation slope with 387.1 dB/GHz in the lower and 462.3 dB/GHz in the upper transition bands) and wide stopband up to 3.88f0.