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Analysis of Novel Approach to Design of Ultra-wide Stopband Microstrip Low-Pass Filter Using Modified U-Shaped Resonator

  • Karimi, Gholamreza (Department of Electrical Engineering, the Faculty of Engineering, Razi University) ;
  • Lalbakhsh, Ali (Department of Engineering, Kermanshah Branch, Islamic Azad University) ;
  • Dehghani, Khatereh (Department of Electrical Engineering, Kermanshah Branch, Islamic Azad University) ;
  • Siahkamari, Hesam (Department of Electrical Engineering, the Faculty of Engineering, Razi University)
  • Received : 2014.02.13
  • Accepted : 2015.05.20
  • Published : 2015.10.01
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Abstract

A novel microstrip low-pass filter is presented to achieve an ultra-wide stopband with 11 harmonic suppression and very sharp skirt characteristics. The filter is composed of a modified U-shaped resonator (which creates two fully adjustable transmission zeroes), a T-shaped resonator (which determines a cut-off frequency), and four radial stubs (which provide a wider stopband). The operating mechanism of the filter is investigated based on a proposed equivalent-circuit model, and the role of each section of the proposed filter in creating null points is theoretically discussed in detail. The presented filter with 3 dB cut-off frequency ($f_c=2.35GHz$) has been fabricated and measured. Results show that a relative stopband bandwidth of 164% (referred to as a 22 dB suppression) is obtained while achieving a high figure-of-merit of 15,221.

Keywords

References

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