Hybrid Microstrip/DGS Cell for Filter Design

In this letter, a compact bandpass filter is proposed based on the hybrid microstrip/defected ground structure (DGS) cells with an interdigital-coupled (IC) scheme. The hybrid cell can employ two functions for the filter: 1) dual-resonances operation and 2) two close transmission zeros around the resonances. With a proper coupled scheme (i.e., the IC scheme), the narrow-band coupling for the passband enhancement of high selectivity and wide stopband can be achieved. Then, a filter operated at 2.455 GHz (i.e.,
f
₀
) is fabricated, which shows the strong attenuation slope with 427.2 dB/GHz in the lower and 779.1 dB/GHz in the upper transition bands and a wide stopband up to 3.56
f
₀
.