A wide bandpass filter with defected ground structure for wide out-of-band suppression

This paper presents a wide bandpass filter (BPF) with low insertion loss and excellent harmonic out-of-band suppression over a very wideband. The filter consists of a standard ultra-wideband bandpass filters design approach combined with periodic defected ground structure (DGS), which is able to inhibit signal propagation over a wideband. To realize this filter, a wideband microstrip BPF with a bandwidth covering 3.7 GHz is implemented in an RO4350 substrate (ε_r = 3.66, h = 0.762 mm). This bandpass filter shows a wide bandwidth with measured insertion loss better than 0.9dB and spurious suppression better than 24 dB.