In this paper, the design of compact and high performance parallel coupled line wideband bandpass filter using image parameter method are proposed. The filter mainly comprising one-stage parallel coupled line and two open stubs are designed and implemented on commercial RT/Duroid 5880 substrate. The equivalent circuit of the proposed structure is initially derived by using the image parameter method. It is found that, the normalized bandwidth (NBW) of image impedance for the one-stage parallel coupled line has a relation to the electromagnetic (EM) simulated bandwidth. To further improve the selectivity, two open stubs are connected near the input/output (I/O) ports. The design procedures and their limitations are discussed in detail. The proposed filters are fabricated, measured and showing good characteristics of 87% fractional bandwidth as well as good insertion/return loss, flat group delay varies between 0.3-1.5 ns. High passband selectivity and wide stopband from 8-14 GHz are obseved. The measured results are also having a good agreement with the simulated results.
2. Chang, D. C. and C. W. Hsue, "Wide-band equal-ripple filters in nonuniform transmission lines," IEEE Trans. Microw. Theory Tech., Vol. 50, No. 4, 1114-1119, 2002.
3. Chen, C. C., J. T. Kuo, M. Jiang, and A. Chin, "Study of parallel coupled-line microstrip filter in broadband," Microw. Opt. Tech. Lett., Vol. 48, No. 2, 373-375, 2006.
4. Chin, K. S., L. Y. Lin, and J. T. Kuo, "New formulas for synthesizing microstrip bandpass filters with relatively wide bandwidths," IEEE Microw. Wireless Compon. Lett., Vol. 14, No. 5, 231-233, 2004.
5. Shobeyri, M. and M. H. Vadjed-Samiei, "Compact ultra-wideband bandpass flter with defected ground structure," Progress In Electromagnetics Research Letters, Vol. 4, 25-31, 2008.
6. Naghshvarian-Jahromi, M. and M. Tayarani, "Miniature planar UWB bandpass filters with circular slots in ground," Progress In Electromagnetics Research Letters, Vol. 3, 87-93, 2008.
7. Wei, F., P. Chen, L. Chen, and X. W. Shi, "Design of a compact UWB bandpass filter with defected ground structure," Journal of Electromagnetic Waves and Applications, Vol. 22, No. 13, 1783-1790, 2008.
8. Wu, B., X. Lai, T. Su, and C. H. Liang, "Wideband cross coupled filter using split-ring resonator defected ground structure," Journal of Electromagnetic Waves and Applications, Vol. 22, 1631-1638, 2008.
9. An, J., G.-M. Wang, W.-D. Zeng, and L.-X. Ma, "UWB flter using defected ground structure of Von Koch fractal shape slot," Progress In Electromagnetics Research Letters, Vol. 6, 61-66, 2009.
10. Zhu, L., S. Sun, and W. Menzel, "Ultra-wideband (UWB) bandpass filters using multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 15, No. 11, 796-798, 2005.
11. Sun, S. and L. Zhu, "Capacitive-ended interdigital coupled lines for UWB bandpass filters with improved out-of-band performances," IEEE Microw. Wireless Compon. Lett., Vol. 16, No. 8, 440-442, 2006.
12. Li, R. and L. Zhu, "Compact UWB bandpass filter using stub-loaded multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 1, 40-42, 2007.
13. Shaman, H. and J. S. Hong, "A novel ultra-wideband (UWB) bandpass filter (BPF) with pairs of transmission zeroes," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 2, 121-123, 2007.
14. Hung, C. Y., M. H. Weng, R. Y. Yang, and Y. K. Su, "Design of the compact parallel coupled wideband bandpass filter with very high selectivity and wide stopband," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 7, 510-512, 2007.
15. Pozar, D. M., Microwave Engineering, Wiley, Hoboken, 2005.
16. Kirschning, M. and R. H. Jansen, "Accurate wide-range design equations for the frequency-dependent characteristic of parallel coupled microstrip lines," IEEE Trans. Microw. Theory Tech., Vol. 32, No. 1, 83-90, 1984.
17. Zeland Software, Inc., IE3D Simulator, 1997., 1997.
18. Hsieh, L. H. and K. Chang, "Compact, low insertion-loss, sharprejection, and wide-band microstrip bandpass filters," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 4, 1241-1246, 2003.
19. Tu, W. H. and K. Chang, "Compact second harmonic-suppressed bandstop and bandpass filters using open stubs," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 6, 2497-2502, 2006.
20. Hung, C. Y., M. H. Weng, Y. K. Su, and R. Y. Yang, "A simple method to design a compact and high performance wideband filter," Microw. Opt. Tech. Lett., Vol. 49, No. 4, 822-824, 2007.