His page on variable inductors had me going "ohhh" quite a few times.

If anybody knows about non mechanical / solid state variable caps / inductors, I was trying to find how to learn about them.

Electrically controllable inductors are known as saturable reactors. One quite interesting use is in the tuning of a synchrotron accelerating cavity.

Here is a paper on using varactors to tune a loop antenna:

http://home.earthlink.net/~christrask/Varactor%20Tuned%20Loo...

He also has many other good papers on RF.

Thanks that's exactly the kind of terminology I was lacking :)

> solid state variable caps

Varicaps are only good for low power and are kind of nonlinear, but it's a voltage controlled capacitance.

I think for lower frequencies, a capacitor bank that's switched is the best bet.

In terms of inductors, AFAIK other than an inductor matrix it doesn't exist, but i think you can build a virtual inductor using a GIC.

Peregrine makes several digitally tunable capacitors (switched capacitor banks) that work to S-band and can handle moderate power. I have used them for antenna tuning.

https://www.psemi.com/products/digitally-tunable-capacitors-...

Diodes exhibit capacitance that varies with respect to their DC bias. I know this is used in GHz RF applications.

Using opamps to create virtual reactive components (capacitors, or inductors) that would otherwise be impractical to build directly (too high of value) is an interesting trick.

> Diodes exhibit capacitance that varies with respect to their DC bias. I know this is used in GHz RF applications.

Oops, I meant to say varactor, not varicap. And this is used for VHF and up as well.

The GIC-based filters are used a lot for high-Q parametric filters often in audio or general scientific stuff.

Thanks for reminding me about this. His whole website is practically a reference text for RF engineering, now is the perfect time to dive back in.

You can also simulate these kind of experiments using EM solvers.

Are there any particular ones that you would recommend?

I use CST often, and used it for helical resonators, specifically the Eigenmode solver. The latest version should do an eigenmode analysis with open boundaries, which you’d need for coils. My resonator was in a cavity.