Miniaturization of lowpass filters by using artificial transmission lines

In this paper, a miniaturization method of lowpass filters by using artificial transmission lines (ATLs) is proposed. Instead of the published lumped element modeling, much more robust modeling of ATL based on ABCD parameters is used for the analysis and design of lowpass filters (LPFs). From two different conventional LPFs based on Richard´s transformation and Kuroda´s identity, miniaturized LPF configurations are derived with main transmission lines and stubs replaced by various ATLs. Two LPFs with a cut-off frequency of 2 GHz and 0.2 dB ripple are designed and fabricated. Reasonable agreement between the measured and the specifications is observed. In addition, two proposed LPF configurations show a size reduction ratio of 29.1% and 37.7%, respectively, compared with the corresponding conventional LPFs.