Dual-mode dual-band bandpass filter (III)
4.6 Comparison of three dual-mode dual-band bandpass filters
Table 4.1 compares the performances and circuit area of three dual-mode dual-band bandpass filters reported in this paper. The first has the smallest circuit area and has relative good rejection between the two passbands. Although the second bandpass filter has the largest circuit area, the isolation between the two passbands is better than -30 dB. In comparison with the second filter, the third one features a lower measured insertion loss at fc1, many more transmission zeros and a smaller circuit area.
Type Filter (I) Filter (II) Filter (III) Center frequencies
fc1 / fc2 (GHz)
2.45 / 5.2 2.45 / 5.8 2.45 / 5.8
Insertion loss (measured, in dB)
2.10 / 1.20 2.15 / 2.91 1.63 / 2.96
Max. Insertion loss (fc1 – fc2)
30 dB 30 dB 15 dB
Number of transmission zeros
4 2 5
Number of via-holes
1 2 1
Circuit area (in mm2)
11.50 × 16.90 15.44 × 21.80 13.84 × 14.34
Table 4.1 Related parameters of three dual-mode dual-band bandpass filters
t
1L ,W t
1t
2L ,W t
2r
W
2W
1W e S
L
cW
cG
L
2L
1e
2L
e
1L
(a)
L L
L
1 1
2
(b)
Fig. 4-1 (a) Circuit layout of the proposed dual-mode dual-band filter. (b) Equivalent circuit of the ground via connected with two short high-impedance sections.
θ
22L2
L1
Yine2
Yine1
Z2 Z1
Z1
θ
1θ
1Z2
θ
2(a)
θ2
L1
Yino2
Yino1
Z2 Z1
Z1
θ1
θ1
Z2
θ2
(b)
Fig. 4-2 (a) Even-mode equivalent circuit of Fig. 4-1(a). (b) Odd-mode equivalent circuit of Fig. 4-1(a)
Frequency (GHz)
Freq. Response (dB) -20
-40
Fig. 4-4 Changes of resonant frequencies with variation of Lt. Detailed parameters are in Fig.
4-9.
1.5
-30
Fig. 4-7 Change of the four transmission zeros versus the length of source-load coupled section, Lc.
Fig. 4-9 Circuit photo. Geometric parameters in mm: L1 = 20.14, W1 = 1.02, L2 = 13.1, W2 = 0.23, Wt1 = Wt2 = 0.3, Lt1 = Lt2 = 0.25, Wc = 0.2, Lc = 0.8, Le1 = 13.24, Le2 = 7.32, We = S = 0.15, G = 0.2, radius = r = 0.2.
Chapter 5 Conclusion
Three dual-mode dual-band bandpass filters with controllable bandwidths are studied in this thesis. The stepped-impedance resonators are used as resonating elements to achieve the dual-band characteristics. By adjusting the inductive and capacitive couplings provided by high-impedance sections and interdigital capacitors, the bandwidth of the two passbands can be well controlled. In addition, additional transmission zeros can be created by employing the source-load coupling and skew symmetric feed structure.
The first dual-mode dual-band bandpass filters composed of a single resonating element are demonstrated. The resonating element is a stepped-impedance resonator with its center being connected to a ground via with a high-impedance section for inductive coupling of the resonant modes. Capacitive coupling is also introduced in shunt with the inductive network for control of the circuit bandwidths at the two designated frequencies. Two extra tunable transmission zeros are created with the source-load coupling by a coupled-line section, leading both passbands to feature quasi-elliptic function responses. Two experimental circuits with different bandwidths are fabricated and measured to demonstrate the design flexibility of the proposed circuit. The simulation and measurement results show good agreement.
The second dual-mode dual-band bandpass filter is demonstrated by alternative
stepped-impedance resonators. To achieve dual-mode operation, the two stepped-impedance resonators are connected to the ground via by two short high- impedance sections. The high-impedance sections and ground via are equivalent to inductors for providing coupling between the resonant modes; therefore, the bandwidths of the two passbands can be controlled by adjusting the inductive coupling. In addition, the skew symmetric feed structure is used to generate two transmission zeros. The simulation and measured data show good agreement.
The third dual-mode dual-band bandpass filter is evolved from the second dual-mode dual-band bandpass filter. In this third dual-mode dual-band bandpass filter, the two ground vias in the previous filter are connected to a single one to ease the fabricated process. A more compact circuit area is obtained at the same time. With the aid of source-load coupling, additional transmission zeros are generated to improved the selectivity of the two passbands.
The simulation and measurement results show good agreement.
References
[1] J.-T. Kuo, T.-H. Yeh and C.-C. Yeh, “Design of microstrip bandpass filters with a dual-passband response,” IEEE Trans. Microwave Theory Tech., vol. 53, no. 11, pp.
1331-1337, Apr. 2005.
[2] J.-T. Kuo and H.-P. Lin, “Dual-band bandpass filter with improved performance in extended upper rejection band,” IEEE Trans. Microwave Theory Tech., vol. 57, no. 4, pp.
824-829, Apr. 2009.
[3] J.-T. Kuo and H.-S. Cheng, “Design of quasi-elliptic function filters with a dual-passband response,” IEEE Microwave Wireless Compon. Lett., vol. 14, no. 10, pp. 472-474, Oct.
2004.
[4] C.-H. Tseng and H.-Y. Shao, “A new dual-band microstrip bandpass filter using net-type resonators,” IEEE Microwave Wireless Compon. Lett., vol. 20, no. 4, pp. 196-198, April.
2010.
[5] G.-L. Dai, Y.-X. Guo and M.-Y. Xia, “Dual-band bandpass filter using parallel short-end feed scheme,” IEEE Microw. Wireles Compon. Lett., vol. 20, no. 6, pp. 325–327, Jun.
2010.
[6] M.-H. Wang, H.-W. Wu and Y.-K. Su, “Compact and low loss dualband bandpass filter using pseudo-interdigital stepped impedance resonators for WLANS,” IEEE Microw.
Wireless Compon. Lett., vol. 17, no. 3, pp. 187–189, Mar. 2007.
[7] X.-Y. Zhang, J.-X. Cheng, Q. Xue and S. M. Li, “Dual-band bandpass filters using stub-loaded resonators,” IEEE Microw. Wireles Compon.Lett., vol. 17, no. 8, pp. 583–585, Aug. 2007.
[8] P. Mondal and M. K. Mondal, “Design of dual-band bandpass filters using stub-loaded open-loop resonators,” IEEE Trans. Microw. Theory Tech., vol. 56, no. 1, pp. 150–154, Jan. 2008.
[9] C.-M. Tsai, H.-M. Lee and C.-C. Tsai, “Planar filter design with fully controllable second passband,” IEEE Trans. Microwave Theory Tech., vol. 53, no. 11, pp. 3429-3439, Nov.
2005.
[10] H.-M. Lee and C.-M. Tsai, “Dual-band filter design with flexible passband and bandwidth selections,” IEEE Trans. Microwave Theory Tech., vol. 55, no. 5, pp.
1002-1009, May. 2007.
[11] J.-X. Chen, T.-Y. Yum, J.-L. Li and Q. Xue, “Dual-mode dual-band bandpass filter using stacked-loop structure,” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 9, pp.
502-504, Sep. 2006.
[12] X. Y. Zhang and Q. Xue, “Novel dual-mode dual-band filters using coplanar-waveguide-fed ring resonators,” IEEE Trans. Microw. Theory Tech., vol. 55, no.
10, pp. 2183-2190, Oct. 2007.
[13] A. Görür and C. Karpuz, “Compact dual-band bandpass filters using dual-mode resonators,” in IEEE MTT-S Int. Dig., Jun. 2007, pp. 905-908.
[14] C. Lugo and J. Papapolymerou, “Multilayer dual-band filter using a reflector cavity and dual-mode resonators,” IEEE Microw. Wireless Compon. Lett., vol. 17, no. 9, pp. 637-639, Sep. 2007.
[15] J.-S. Hong and W. Tang, “Dual-band filter based on non-degenerated dual-mode slow-wave open-loop resonators,” IEEE MTT-S Int. Microwave Symp. Dig., pp. 861–864, Boston, MA, Jun. 2009.
[16] Y.-C. Chiou, C.-Y. Wu and J.-T. Kuo, “New miniaturized dual-mode dual-band ring resonator bandpass filter with microwave C-sections,” IEEE Microwave Wireless Compon. Lett., vol. 20, no. 2, pp. 67-69, Feb. 2010.
[17] T.-W. Lin, U.-H. Lok and J.-T. Kuo, “New dual-mode dual-band bandpass filters with quasi-elliptic function passbands and controllable bandwidths,” in IEEE MTT-S Int. Dig., Jun. 2010, pp. 905-908.
[18] Q.-X. Chu, F.-C. Chen, Z.-H. Tu and H. Wang, “A novel crossed resonator and its applications to bandpass filters,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 7, pp.
1753-1759, Jul. 2009.
[19] P.-H. Deng, Y.-S. Lin, C.-H. Wang and C.-H. Chen, “Compact microstrip bandpass filters with good selectivity and stopband rejection,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 2, pp. 533-539, Feb. 2006.
[20] L. Athukorala and D. Budimir, “Compact dual-mode open loop microstrip resonators and filters,” IEEE Microw. Wireless Compon. Lett., vol. 19, no. 11, pp. 360-362, Nov. 2009.
[21] C.-M. Tsai, S.-Y. Lee and C.-C. Tsai, “Performance of a planar filter using 0o feed structure,” IEEE Trans. Microw. Theory Tech., vol. 50, no. 10, pp. 2362-2367, Oct. 2002.
[22] W.-H. Tu, “Compact dual-mode cross-coupled microstrip bandpass filter with tunable transmission zeros,” Microwaves, Antennas & Propagation, IET , vol. 2, no. 4, pp.
373–377, Jun. 2008.
[23] IE3D Simulator, Zeland Software Inc., Jan. 1997.
[24] I. Bahl, Lumped Elements for RF and Microwave Circuits. Boston, MA: Artech House, 2003, pp. 230–235.
[25] D. M. Pozar, Microwave Engineering, 2nd ed. New York: Wiley, 1998.