In this paper, a novel microwave bandpass filter structure is proposed. By introducing a metallic via hole, the filter structure operates as one λ/2 and two λ/4 uniform impedance resonators and consequently form a triplet coupling scheme. The equivalent circuit model is analyzed in detail, which shows that there is a transmission zero in the low stopband. Based on that concept, three microstrip filters are designed, fabricated and measured, respectively. The first filter has no source/load coupling and only one transmission zero is created. By introducing source/load coupling, the second filter can create three transmission zeros. The third filter can create a controllable transmission zero in upper stopband. The simulated and measured results agree very well.
1. Hong, J.-S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001.
2. Cohn, S. B., "Parallel-coupled transmission-line-resonator filters," IEEE Trans. Microw. Theory Tech., Vol. 6, No. 2, 223-231, Apr. 1958. doi:10.1109/TMTT.1958.1124542
3. Hong, J.-S. and M. J. Lancaster, "Cross-coupled microstrip hairpin-resonator filters," IEEE Trans. Microw. Theory Tech., Vol. 46, No. 1, 118-122, Jan. 1998. doi:10.1109/22.654931
4. Matthaei, G. L., "Interdigital bandpass filter," IRE Trans. Microw. Theory Tech., Vol. 10, No. 6, 41-45, Nov. 1962.
5. Makimoto, M. and S. Yamashita, "Bandpass filters using parallel coupled stripline stepped impedance resonators," IEEE Trans. Microw. Theory Tech., Vol. 28, No. 12, 1413-1417, Dec. 1980. doi:10.1109/TMTT.1980.1130258
6. Chen, C. C., Y. R. Chen, and C. Y. Chang, "Miniaturized microstrip cross-coupled filters using quarter-wave or quasi-quarter-wave resonators," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 1, 120-131, Jan. 2003. doi:10.1109/TMTT.2002.806924
7. Lin, S. C., Y. S. Lin, and C. H. Chen, "Extended-stopband bandpass filter using both half- and quarter-wavelength resonators," IEEE Microw. Wireless Compon. Lett., Vol. 51, No. 1, 120-131, Jan. 2003.
8. Deng, P. H., C. H. Wang, and C. H. Chen, "Novel broadside-coupled bandpass filters using both microstrip and coplanar-waveguide resonators," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 10, 3746-3750, Oct. 2006. doi:10.1109/TMTT.2006.881619
9. Goldfarb, M. E. and R. A. Pucel, "Modeling via hole grounds in microstrip," IEEE Microwave Guided Wave Lett., Vol. 1, No. 6, 135-137, Jun. 1991. doi:10.1109/75.91090
10. Sato, R. and E. G. Cristal, "Simplified analysis of coupled transmission ine networks," IEEE Trans. Microw. Theory Tech., Vol. 18, No. 3, 122-131, Mar. 1970. doi:10.1109/TMTT.1970.1127172
11. Nemoto, Y., K. Kobayashi, and R. Sato, "Graph transformations of nonuniform coupled transmission line networks and their application," IEEE Trans. Microw. Theory Tech., Vol. 33, No. 11, 1257-1263, Nov. 1985. doi:10.1109/TMTT.1985.1133208
12. Ozaki, H. and J. Ishii, "Synthesis of a class of strip-line filters," IRE Trans. Circuit Theory, Vol. 5, No. 2, 104-109, Jun. 1958.
13. Mohd Salleh, M. K., G. Prigent, O. Pigaglio, and R. Crampagne, "Quarter-wavelength side-coupled ring resonator for bandpass filters ," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 1, 156-162, Jan. 2008. doi:10.1109/TMTT.2007.912167
14. Wadell, B. C., Transmission Line Design Handbook, Norwood, USA, 1991.
15. Rosloniec, S., "Algorithms for Computer-aided Design of Linear Microwave Circuits ," Norwood, USA, 1990.
16. Hunter, I., "Theory and design of microwave filters," IEE Electromagnetic Waves Series, 2001.
17. Ismail, A., M. S. Razalli, M. A. Mahdi, R. S. A. Raja Abdullah, N. K. Noordin, and M. F. A Rasid, "X-band trisection substrate-integrated waveguide quasi-elliptic filter," Progress In Electromagnetics Research, Vol. 85, 133-145, 2008. doi:10.2528/PIER08081802
18. Tsai, C. M., S. Y. Lee, and H. M. Lee, "Transmission-line filters with capacitively loaded coupled lines," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 5, 1517-1524, May 2003. doi:10.1109/TMTT.2003.810133