Design of Planer type Comb-Line Bandpass Filter And Design Parameter Extraction Using FE Analysis

In this paper, we present a design procedure of comb-line bandpass filter with asymmetrical coupled-lines, which has small size in comparison with other planar type filters to take full advantage of reducing the size of RF and microwave components. Based on a parallel coupled-line theory, we develop admittance inverter model for each asymmetric coupled-line pair. By combining equivalent circuits of the coupled-line section, the design formula, which means the J-inverter formula, for the presented filter is derived. Furthermore, a simple approach using 2-D static FE calculations is employed to extract the physical dimensions of asymmetric coupled-line for a comb-line band-pass filter. Fourth order comb-line bandpass filter with a microstrip multiple coupled-lines is designed by the aforementioned method. In addition, the comb-line filter has been simulated with 3-D EM software and fabricated for measurements. Excellent agreement between the simulation and measurement on the design filter shows the validity of the presented design and design-parameter extraction methods.