Just curious... how do tuneable filters, oscillators, phase shifters, etc.
made from Yttrium Iron Garnet (YIG) materials work? Does an applied DC
magnetic field alter the effective permeability of the material? Or is
something more complex going on?

Also... what tends to limit YIG devices to not typically be used much below
some "many hundreds" MHz? Is it just loss in the material starts to become
prohibitive? Or something else?

I've done a little Googling, and although there's a lot about YIGs out there,
it's usually at either a much lower level or much higher level than what I'm
after here!

Thanks,
---Joel Kolstad