A compact narrow band microstrip bandpass filter with defected ground structure (DGS)

In this paper, a compact narrow band bandpass filter is proposed with hexagonal dumbbell shaped defected ground structure in ground plane of a 50Ω microstrip line and a closed loop resonator in the conducting strip. This arrangement provides better coupling in pass band. Using DGS structure, forward transmission loss (S₂₁) is -0.5 dB and return loss (S₁₁) is -26.7 dB at the centre frequency 5.4 GHz with narrow bandwidth of 500 MHz. A conventional parallel coupled line bandpass filter has also been implemented with exactly same design goals for the sake of comparison. The proposed bandpass filter with DGS is quite promising with 60% size reduction.