Design and Transformation of a Miniature LPF to a BSF Filter Using Modified Stepped Impedance

Abstract

In this paper, a design and transformation of a miniature LPF to a BSF using modified stepped impedance is presented. The filter is mounted on a flame retardant-4 substrate having a thickness of 1.6 mm, a dielectric constant of 4.4 and loss tangent of 0.025. Design a stepped-impedance Low Pass Filter with a maximally flat response and a cut-off frequency of 5.8 GHz. The filter should have more than 25 dB insertion loss at 7 GHz. The filter impedance is 50 Ω, with the highest practical line impedance being 120 Ω and the lowest being 20 Ω. This circuit is designed and simulated by using two electromagnetic solvers based on different physical methods. The addition of split ring resonators SRR to the previously designed filter results in the transformation of the LPF into a band-stop filter, with cut-off frequencies: 3.23GHz and 3.98GHz, Amax ripple = 1.367 dB in bandwidth, and 19.57 dB attenuation at Frequency 3.5GHz. This filter features a stopband fractional bandwidth of 21.4%. This study aims to contribute to the advancement of a compact microstrip Low Pass Filter and, Band Stop Filter with superior electrical performance.