This paper proposes a compact microstrip bandpass filter (BPF) with high selectivity. A folded stepped-impedance resonator (SIR) of which the high impedance part is realized by a coplanar waveguide on the ground layer is introduced to the filter design for miniaturization. Furthermore, source-load coupling is implemented by extended tapped lines (ETLs). High selectivity with four transmission zeros (TZs) can be achieved. The analysis of the filter is presented based on atransmission line circuit model and even- and odd-mode analysis method. An experimental filter with the size of 0.15λg*0.13λg (where λg is the guide wave-length at the center frequency) is designed to validate our methods.
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doi:10.1049/el.2016.4215
3. Wu, C. H., C. H. Wang, Y. S. Lin, and C. H. Chen, "Parallel-coupled coplanar-waveguide bandpass filter with multiple transmission zeros," IEEE Microwave and Wireless Components Letters, Vol. 17, No. 2, 118-120, 2007.
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5. Li, L. and Z. F. Li, "Application of inductive source-load coupling in microstrip dual-mode filter design," Electronics Letters, Vol. 46, No. 2, 141-142, 2010.
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6. Dai, G. L., Y. X. Guo, and M. Y. Xia, "Design of compact bandpass filter with improved selectivity using source-load coupling," Electronics Letters, Vol. 46, No. 7, 505-506, 2010.
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7. Xu, Z. Q., P. Wang, K.W. Qian, and Z. Tian, "Substrate integrated waveguide filter with embedded mixed source-load coupling," Electronics Letters, Vol. 49, No. 23, 1464-1465, 2013.
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9. Deng, H. W., F. Liu, T. Xu, L. Sun, and Y. F. Xue, "Compact and high selectivity dual-mode microstrip BPF with frequency-dependent source-load coupling," Electronics Letters, Vol. 54, No. 4, 219-221, 2018.
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10. Li, L. and Z. Li, "Side-coupled shorted microstrip line for compact quasi-elliptic wideband bandpass filter design," IEEE Microwave and Wireless Components Letters, Vol. 20, No. 6, 322-324, 2010.
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11. Zhu, L., S. Sun, and R. Li, Microwave Bandpass Filters for Wideband Communications, Chapters 2 and 3, 18–84, John Wiley & Sons. Inc., 2012.
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