Design concept for microwave recursive and transversal filters using Lange couplers

The authors focus on the use of Lange couplers in the design of passive recursive and transversal filters in the microwave frequency range. A simple numerical method for the computation of the filter parameters is described. A synthesis example is given to illustrate the techniques for the wideband filter case. It is shown that Lange couplers can be effectively employed in the design of recursive and transversal filters. Analytical, computer-simulated, and experimental results are preserved for two passive bandpass filters which were implemented on a Duroid substrate in the 3-5-GHz frequency range. Good agreement was obtained between the theoretical and the measured S-parameters for the filters.<>