Ktechlab might be a bit more popular than QUCS. We know about 1 link to it since March 2021 and only 1 link to QUCS. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
If you can get s parameter model you can use that. There are also generic transformer and coupled line models so long as you've got a way of characterising it you should be able to model it. https://sourceforge.net/projects/qucs/. Source: about 1 year ago
I found ktechlab and QUCS, both of them are Open Source. Source: almost 2 years ago
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