Design and Optimization of Microstrip Parallel-Coupled-Line Bandpass Filters Incorporating Impedance Matching

Homayoon ORAIZI  Mahdi MORADIAN  Kazuhiro HIRASAWA  

IEICE TRANSACTIONS on Communications   Vol.E89-B   No.11   pp.2982-2989
Publication Date: 2006/11/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.11.2982
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Devices/Circuits for Communications
filter,  microstrip parallel-coupled-line,  impedance matching,  method of least squares,  optimization,  

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In this paper a new method for the design and optimization of microstrip parallel coupled-line bandpass filters is presented which allows for the specification of frequency bandwidths and arbitrary source and load impedance transformation. The even- and odd-mode theory and the relationships between impedance, transmission and scattering matrices and their properties are used to construct a positive definite error function using the insertion losses at discrete frequencies in the pass, transition and stop bands. The dispersion relations for the coupled line are also taken into account. The minimization of the error function determines the widths, gap spacings and lengths of the coupled-line filter, for the optimum design and realization of filter specifications. The proposed filter design and optimization method is coded by computer programs and the results of simulation, fabrication and testing of sample filters together with comparisons with available full-wave analysis softwares, indicate the efficacy of the proposed method. Filter design with up to 50% bandwidth and the design of shorter lengths of coupled line sections are achievable by the proposed method in part due to the incorporation of impedance matching.