A compact UWB bandpass filter using hybrid fractal shaped DGS

Abstract

In this paper, a novel and compact ultra wideband (UWB) bandpass filter (BPF) based on fractal-shaped defected ground structure (DGS) is designed and developed. It is made of stepped impedance lines and a composite right/left handed-transmission line (CRLH-TL) constructed with capacitive gap in conductor strip and a hybrid fractal-shaped ring slot in ground plane. The capacitive gap between conductor strip and fractal shaped DGS play the major role for controlling the lower and upper passband cutoff frequencies. The prototype of proposed filter is fabricated and measured. Good agreement is found between simulated and measured results. The proposed UWB bandpass filter has good passband performance with 10 dB return-loss bandwidth of 2.2 to 10.6 GHz, insertion loss better than 1.1 dB and fractional bandwidth of 131%. Also, the proposed filter obtained a very wide upper-stopband from 11.4 GHz to beyond 20 GHz with rejection skirt better than 30 dB at both the lower and upper passband cutoff frequencies. Moreover, UWB BPF also shows the flat group delay performance with variation ≤ 0.75 ns in the entire passband. Thus the proposed filter can be a useful candidate for low profile future wireless communication systems.