A compact, ultra-broadband coplanar-waveguide (CPW) bandpass filter (BPF) is demonstrated. The proposed CPW-BPF is essentially designed by exploiting CPW short-stub and open-stub structures. Technically, the proposed filter comprises shunt short-stub and series open-stub structures that are connected in a cascade topology. The higher and lower cutoff frequencies are mainly related to the electrical length of the shunt short stub and the series open stub, respectively. In addition, the stopband rejection is enhanced through an incorporation of CPW bandstop structures. The proposed filter design is verified through experimental demonstration. The corresponding lumped equivalent and transmission-line equivalent circuits are provided for circuit design purpose. Compared with the classical CPW-BPFs, the proposed filter is of a relatively simple and compact configuration. The demonstrated CPW-BPF has about 110% 3-dB fractional bandwidth, sharp selectivity, and great stopband rejection.
2. Razalli, M. S., A. Ismail, M. A. Mahdi, and M. N. Bin Hamidon, "Novel compact microstrip ultra-wideband filter utilizing short-circuited stubs with less vias," Progress In Electromagnetics Research, Vol. 88, 91-104, 2008.
3. Razalli, M. S., A. Ismail, M. A. Mahdi, and M. N. Bin Hamidon, "Novel compact "via-less" ultra-wide band filter utilizing apacitive microstrip patch," Progress In Electromagnetics Research, Vol. 91, 213-227, 2009.
4. Hong, J.-S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001.
5. Lin, F. L., C. W. Chiu, and R. B. Wu, "Coplanar waveguide bandpass filter --- A ribbon-of-brick-wall design," IEEE Trans. Microw. Theory Tech., Vol. 47, 1589-1596, 1995.
6. Kuo, Y.-K., C.-H. Wang, and C. H. Chen, "Novel reduced-size coplanar-waveguide bandpass filters," IEEE Microw. Wireless Compon. Lett., Vol. 11, No. 2, 65-67, 2001.
7. Lin, Y.-S., W.-C. Ku, C.-H. Wang, and C. H. Chen, "Wideband coplanar-waveguide bandpass filters with good stopband rejection," EEE Microw. Wireless Compon. Lett., Vol. 14, No. 9, 422-424, 2004.
8. Gao, J., L. Zhu, W. Menzel, and F. Bogelsack, "Short-circuited CPW multiple-mode resonator for ultra-wideband (UWB) bandpass filter," IEEE Microw. Wireless Compon. Lett., Vol. 16, No. 3, 104-106, 2006.
9. Chen, N.-W. and K.-C. Fang, "An ultra-broadband coplanar waveguide bandpass filter with sharp skirt selectivity," IEEE Microw. and Wireless Compon. Lett., Vol. 17, No. 2, 124-126, 2007.
10. Dib, N. I., L. P. B. Katehi, G. E. Ponchak, and R. N. Simons, "Theoretical and experimental characterization of coplanar waveguide discontinuities 49-53 for filter applications," IEEE Trans. Microw. Theory Tech., Vol. 39, 873-881, 1991.
11. Simons, R. N., Coplanar Waveguide Circuits, Components, and Systems, Wiley Interscience, 2001.
12. Liu, A. Q., A. B. Yu, and Q. X. Zhan, "Broad-band band-pass and band-stop filters with sharp cut-off frequencies based on series CPW stubs," IEEE MTT-S Int. Microwave Symp. Digest, 353-356, 2006.