![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
Abstract
In this paper, a compact third-order bandpass filter with enhanced stopband characteristics is proposed. The filter consists of three stepped impedance resonators, where one is embedded into the other two resonators for compact size. Multiple transmission zeros (TZs) can be realized near the passband by introducing frequency-dependent coupling between the nonadjacent resonators for enhanced frequency selectivity. Besides, defected ground structure is employed to suppress the harmonics over a broad bandwidth. A new filter centered at 1.51 GHz has been analyzed, simulated, and fabricated to verify the validity of the proposed method. The measured results show that there are three finite TZs near the passband, which are located at 1.1 GHz with 62.1 dB rejection, 1.76 GHz with 34.2 dB rejection, and 2.48 GHz with 37.2 dB rejection, respectively. And, the spurious frequencies of the upper stopband are suppressed below 20 dB from 1.7 to 25 GHz.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (51172034) and the Fundamental Research Funds for the Central University of UESTC (ZYGX2010J120).