Miniaturization of stepped-impedance low-pass filters using periodical structures

This paper proposes a design to reduce the size of traditional stepped-impedance low-pass filters and a solution to the discontinuity problem encountered in the original design. In this design, the low-impedance sections of the traditional design are replaced by periodical structures with shunt elements. The structure itself features size reduction and the new characteristic impedance is made equal to that of the high-impedance sections to eliminate the problem of discontinuity. A six-section design example is presented with its 3-dB cutoff frequency set at 2.5 GHz. The ADS simulation results show good agreement between the traditional design and the proposed design. The latter offers more than 40% in size reduction compared to the former. The simulation results are verified experimentally. Good agreement is observed.