Interdigital Filter

Interdigital Bandpass Filters
Joachim Köppen DF3GJ ... Kiel, July 2016

This tool is the JavaScript version of N6JH's BASIC program (HamRadio, Jan 1985, p.12) and its C++ version by WA4DSY (1997), which follow the FORTRAN program INTFIL by Rook and Taylor (1970).
The filter type is Chebychev (specify ripple in dB) or Butterworth (ripple=0).
Enter the design data in the text fields, and hit the Enter key or the compute button. If the bandwidth is too small or too large for the approximations used in the program, its text field appears yellow as a warning that the results are less reliable.
The program will happily design filters with as many rods as you might wish ... but be aware that the inevitable losses will not make it possible to build real filters with more than about 20 elements!
The plot shows the frequency response of the filter. The user may chose a different frequency span for the display.
The table below the plot summarizes all design parameters and the mechanical details of the filter