A Novel Method for the Design and Optimization of Microstrip Multi-section Bandpass Combline Filters

A novel least square based method is developed for the microstrip multi-section bandpass combline filter. First, the overall transmission matrix of the filter is obtained in terms of its various geometrical dimensions. The effects of couplings among adjacent and nonadjacent coupled conducting strips and also the dispersion relations of coupled lines on microstrips are considered. Then, the filter scattering parameters and its insertion loss is determined. Subsequently, an error function is constructed based on the optimization of specified insertion losses in the passband, transition bands and stopbands. The performance of the proposed least square method for the combline filter design and optimization is verified by the available electromagnetic software packages, which highlights its several advantages (such as simultaneous input and output impedance matching) compared with the available design procedures