Advanced Electromagnetics (Sep 2018)

A New Lowpass Filter Unit Cell with Sharp Roll-off and Improved Stopband Performance in Coplanar Waveguide Technology

  • A. Bijari,
  • M. Mohebrad

DOI
https://doi.org/10.7716/aem.v7i5.901
Journal volume & issue
Vol. 7, no. 5
pp. 14 – 19

Abstract

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In this paper, a new compact unit cell for a coplanar waveguide (CPW) lowpass filter (LPF) is proposed. By combining a pair of coupled parallel stepped impedance resonators (SIRs) and high impedance short stubs in the CPW line, a fifth-order elliptic lowpass filter unit cell (LUC) is designed. The extra transmission zero introduced by parallel coupled SIRs is used to extend the stopband and increase the roll-off rate. The characteristics of the proposed LUC is investigated to achieve a sharp roll-off and a wide stopband. The measured results are in accordance with the simulated results. It has an insertion loss less than 0.9 dB from dc to 6 GHz, and a wide -15 dB stopband from 7.5 to 18 GHz. In addition, the filter dimensions are as small as 4.9 mm × 8.7 mm, that is, 0.046λg2, where λg is the guided wavelength at the cut-off frequency. The filter structure is simple and easy to fabricate as well.

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