This paper presents a novel spurious suppressed bandpass filter designed with triangular stepped-impedance resonators. The proposed resonators are folded for a triangular schematic, which creates two transmission zeros. By varying the line width of resonators, one of the zeros is tuned to suppress the first and second spurious responses, and the other is used to improve skirt selectivity. The current study analytically derives explicit design equations and fabricates a three-pole Chebyshev bandpass filter centered at 1.5 GHz based on the direct-coupled structure. The experimental results show spurious suppression improvement more than 20 dB up to 5.6 f0.
2. Sagawa, M., K. Takahashi, and M. Makimoto, "Miniaturized hairpin resonator filters and their application to receiver front-end MIC's," IEEE Trans. Microwave Theory Tech., Vol. 37, 1991-1996, Dec. 1989.
3. Ma, K., K. S. Yeo, J. Ma, and M. A. Do, "An ultra-compact hairpin band pass filter with additional zero points," IEEE Microwave and Wireless Components Letters, Vol. 17, 262-264, Apr. 2007.
4. Adam, H., A. Ismail, M. A. Mahdi, M. S. Razalli, A. R. H. Alhawari, and B. K. Esfeh, "X-band miniaturized wideband bandpass ¯lter utilizing multilayered microstrip hairpin resonator," Progress In Electromagnetics Research, Vol. 93, 177-188, 2009.
5. Lee, S.-Y. and C.-M. Tsai, "New cross-coupled filter design using improved hairpin resonators," IEEE Trans. Microwave Theory Tech., Vol. 48, 2482-2490, Dec. 2000.
6. Hong, J. S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, John Wiley & Sons Inc., 2001.
7. Hong, J. S. and M. J. Lancaster, "Theory and experiment of novel microstrip slow-wave open-loop resonator filters," IEEE Trans. Microwave Theory Tech., Vol. 45, 2358-2365, Dec. 1997.
8. Velazquez-Ahumada, M. C., J. Martel, and F. Medina, "Parallel coupled microstrip filters with ground-plane aperture for spurious band suppression and enhanced coupling," IEEE Trans. Microwave Theory Tech., Vol. 52, 1082-1086, Mar. 2004.
9. Tu, W.-H. and K. Chang, "Compact microstrip bandstop filter using open stub and spurline," IEEE Microwave and Wireless Component Letters, Vol. 15, 268-270, Apr. 2005.
10. Wu, C.-H., Y.-S. Lin, C.-H. Wang, and C.-H. Chen, A compact LTCC ultra-wideband bandpass filter using semi-lumped parallel-resonance circuits for spurious suppression, European Microwave Conference 2007, 532-535, Munich, Germany, Oct. 9-12, 2007.
11. Wang, C.-H., P.-H. Deng, and C.-H. Chen, "Coplanar-waveguide-fed microstrip bandpass filters with capacitively broadside-coupled structures for multiple spurious suppression," IEEE Trans. Microwave Theory Tech., Vol. 55, 768-775, Apr. 2007.
12. Chin, K.-S., Y.-C. Chiang, and J.-T. Kuo, "Microstrip open-loop resonator with multi-spurious suppression," IEEE Microwave and Wireless Components Letters, Vol. 17, 574-576, Aug. 2007.
13. Chaimool, S., S. Kerdsumang, and P. Akkaraekthalin, "A novel microstrip bandpass filter using triangular open-loop resonators," Asia-Pacific Conference on Communications 2003, 788-791.
14. Gorur, A. and C. Karpuz, Cross-coupled bandpass filter using microstrip triangular open-loop resonators, European Microwave Conference 2001, Vol. 1, No. 4, London, England, Oct. 2001.
15. Zhang, J., J.-Z. Gu, B. Cui, and X.-W. Sun, "Compact and harmonic suppression open-loop resonator bandpass filter with tri-section SIR," Progress In Electromagnetics Research, Vol. 69, 93-100, 2007.