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 pro posed. 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., /o) 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.