Design of Low-Pass Filters via Distributed Simplified Real Frequency Technique

This paper presents the method to design low-pass filters (LPFs) via distributed simplified real frequency technique (SRFT). The filters are constructed with series and parallel commensurate transmission lines. With the filter specifications, the synthesizing procedure of topologies can be realized in MATLAB programs. In this work, the pass band of filters is set as DC-1.6 GHz, with the in-band return loss of less than -20 dB and the rejection of 30 dB at 3 GHz. The number of commensurate transmission lines is selected as 6. Four filters with different topologies are obtained by the programs, and the filters are simulated in circuit simulation tool to verify the theoretical synthesizing procedure.