Wide stopband bandpass filter based on DGS slot structure

A novel bandpass filter with excellent harmonic suppression performance based on dual-plane defected ground structure (DGS) is proposed. The DGS slot structure consists of two folded square loop slots and two J-shaped slots. Using this structure, the filter has a good selectivity and exhibits a wide upper stopband characteristic. The equivalent circuit is also presented in this letter. Measured results show that the filter centred at 1.575 GHz has a fractional bandwidth of about 9.2%. The attenuation is below 20 dB over a wide band from 2.2 to 20 GHz.