I’ve been sitting on this code for over 10 years now, and decided last night to vibe code a user interface for it. It uses the ideal transmission line equations, and the units are arbitrary. You’ll have to convert the transmission line lengths (in 1/4 wave segment units) and impedances (ohms) to stub length and width using a tool like wcalc. https://wcalc.sourceforge.net/
The software can be downloaded here:
https://github.com/jcrookswy/Distributed-Element-Filter-Design
Unzip to the folder of your choice. A couple of examples are included. You might have to turn down your security settings to run this unverified application.
The optimizer only tweaks the trace impedances, so you may need to manually tweak trace lengths to get the desired performance.
I added a fun element, the “step shunt”
This can be really useful for pushing a filter’s re-entry to higher frequencies. Of course, a butterfly stub would be even better…
Another great free tool, especially for narrowband band pass filters, is Marki’s:
https://markimicrowave.com/technical-resources/tools/microstrip-filter-design-tool
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