The Design of Two-Section Symmetrical Zobel Filters for Tchebycheff Insertion Loss

It is shown that the complete Tchebycheff insertion-loss function giving equal valley heights in the stop band and equal ripple heights in the pass band can be realized with two Zobel m-derived sections by suitable choice of the m values and the terminating resistance. The limitation in comparison with more general synthesis techniques is that for each width of the cutoff region only one Tchebycheff-Zobel filter is possible, having a fixed value of passband ripple. The ripple levels obtained, however, are in the range of interest and the filters are of practical value. Data are given in chart and tabular form so that the design procedure is very simple. The results show that prototype sections do not appear in the optimum designs, and that terminating half sections need not be used to obtain flat pass-band transmission.