A compact planar ultra-wideband bandpass filter using cross-coupling SIR and defected ground structure

In this paper, an ultra-wideband (UWB) band-pass filter (BPF) for wireless communications is proposed. The band-pass filter consists of a stepped impedance resonator (SIR) with input-output cross-coupling. Additional rectangle-slot defected ground structure (DGS) is employed to improve the attenuation performance in the stop band and generate a strong coupling improving the pass-band property of the coupled lines. The resonance frequencies of the degenerate modes can be adjusted easily to satisfy the wanted bandwidth of the BPF. A parallel-coupling feed structure with a cross coupling has been used to generate two transmission zeros at the lower and upper stop-band, which can improve the out-of-band performance. The filter is simulated by 3D EM commercial software HFSS, the simulated results show that the presented BPF covers the frequency range from 2.7-10.2 GHZ defined by |S11| <; -10 dB. Within the bandwidth, the insertion loss is below 2 dB.