Design of Dual-Band Bandpass Filters for Cognitive Radio Application of TVWS Band

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  • ABSTRACT

    This paper presents a novel design for dual-band bandpass filters. The proposed filters are applicable to the carrier aggregation of the TV white space (TVWS) band and long-term evolution (LTE) band for cognitive radio applications. The lower passband is the TVWS band (470–698 MHz) whose fractional bandwidth is 40 %, while the higher passband is the LTE band (824–894 MHz) with 8 % fractional bandwidth. Since the two passbands are located very close to each other, a transmission zero is inserted to enhance the rejection level between the two passbands. The TVWS band filter is designed using magnetic coupling to obtain a wide bandwidth, and the LTE band filter is designed using dielectric resonators to achieve good insertion loss characteristics. In addition, in the proposed design, a transmission zero is placed with cross-coupling. The proposed dual-band bandpass filter is designed as a two-port filter (one input/one output) as well as a three-port filter (one common input/two outputs). The measured performances show good agreement with the simulated performances.


  • KEYWORD

    Cognitive Radio , Cross Coupling , Dual-Band BPF , TV White Space

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  • [Fig. 1.] Conventional bandpass filter configuration for the TV white space (TVWS) band.
    Conventional bandpass filter configuration for the TV white space (TVWS) band.
  • [Fig. 2.] Bandpass filter with cross couplings between nonadjacent resonators: (a) designed circuit and (b) simulated results.
    Bandpass filter with cross couplings between nonadjacent resonators: (a) designed circuit and (b) simulated results.
  • [Fig. 3.] Designed bandpass filter for the TV white space (TVWS) band with cross couplings.
    Designed bandpass filter for the TV white space (TVWS) band with cross couplings.
  • [Fig. 4.] Frequency responses of two bandpass filters for the TV white space (TVWS) band (solid=with cross couplings, dotted=without cross couplings).
    Frequency responses of two bandpass filters for the TV white space (TVWS) band (solid=with cross couplings, dotted=without cross couplings).
  • [Fig. 5.] Designed LTE-band bandpass filter: (a) conventional circuit and (b) circuit with transmission zeros.
    Designed LTE-band bandpass filter: (a) conventional circuit and (b) circuit with transmission zeros.
  • [Fig. 6.] Simulated frequency performances of Fig. 5(a) and (b).
    Simulated frequency performances of Fig. 5(a) and (b).
  • [Fig. 7.] Designed dual-band bandpass filter (two ports).
    Designed dual-band bandpass filter (two ports).
  • [Fig. 8.] Designed dual-band bandpass filter with a common input port and two output ports (three ports).
    Designed dual-band bandpass filter with a common input port and two output ports (three ports).
  • [Table 1.] Parameter for two-port dual-band bandpass filter
    Parameter for two-port dual-band bandpass filter
  • [Table 2.] Parameter for three-port dual-band bandpass filter
    Parameter for three-port dual-band bandpass filter
  • [Fig. 9.] Simulated and measured S-parameters of proposed two-port dual-band handpass filter.
    Simulated and measured S-parameters of proposed two-port dual-band handpass filter.
  • [Fig. 10.] Simulated and measured S-parameters of proposed three-port bandpass filter.
    Simulated and measured S-parameters of proposed three-port bandpass filter.
  • [Fig. 11.] Photograph of the proposed designs: (a) two-port(3.1 cm × 4.2 cm) and (b) three-port (diplexer; 3.1 cm × 4.2 cm)
    Photograph of the proposed designs: (a) two-port(3.1 cm × 4.2 cm) and (b) three-port (diplexer; 3.1 cm × 4.2 cm)
  • [Table 3.] Performance summaries of the dual-band bandpass filter
    Performance summaries of the dual-band bandpass filter