Electronics > RF, Microwave, Ham Radio

Do any free tools allow you to model RF transformers?

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Basically I want to be able to model transformers - which cannot be done with RFSIM99.

Transmission line or flux-coupled transformer? EM simulation or component simulation?

If it is an 'ideal' transformer then just replace it with an equivalent block in your model accounting for the impedances and such.  If you want parasitics then you'll have to measure or guesstimate them since it is unlikely you'll be able to predict them with a modelling SW.  But once you know the parasitics it's easy to write an equivalent circuit model that includes them and doesn't rely on a transformer block.

If you're just experimenting with transformer construction though it is probably easier just to wind some and test them on your VNA or suitable TE and see how they perform since model driven transformer development isn't usually that helpful.  If you have a particular well characterized transformer in mind then just include the relevant parameters in whatever you're doing with your system level model.

Well, its a toroid core with three windings. Two small and one large. The small ones are the supposed to be 50-or-75-ohm input and output and the larger winding (have tried six to 20 turns, currently using #2 ferrite material..) is a tuned circuit.

It's a long time since I used RFSIM99 but I think it has a transformer model built in?

I've forgotten how well this model works but have you tried stacking several transformers in RFSIM99 to make up an (ideal or physical) equivalent for your three winding transformer? Maybe it won't allow this but in theory you should be able to make up something that resembles your wanted transformer in terms of basic RF performance.

Otherwise, have a look at something like the Simetrix SPICE simulator. The free version is only limited in circuit size and you can select various transformer options including the number of secondaries, the various ratios and also the primary inductance and the coupling factor(s). These are basic models but you can add a few parasitics if you choose.


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