I am designing a current transformer that maybe cannot be done using a single core without switching. I am considering a single- turn primary winding with the secondary winding loaded with a low resistance. I request some advice regarding its design.

I have references indicating that in order to have a maximum accuracy in the ratio and phase angle of the output current the exciting current must be as small as possible. It looks like using a core material with a high permeability and low core loss can do it.

I have observed that some ferrite cores with high permeability (i.e. 300) do not look feasible above maybe 100 MHz. Complex permeability real and imaginary parts cross over at relatively low frequency. Apparently then, the phase error becomes around 45 degrees. It looks like the higher the complex permeability crossing point the lower the operating frequency.

Even though I have references of NiZn ferrite used for RF tuning wideband and balun transformers with permeability around 18 with permeability crossing around 250 MHz.

On the other hand I have seen some iron powder cores ranged to work even up to 500 MHz, from 50 MHz with a permeability of 1.

My question could be if cores with permeability below 300 would work properly as a current transformer (trying to reach the ideal no phase error output current).

May somebody please give me some advices, notes or simulation tools for this 500 kHz-500 MHz current transformer?

Thank you in advance.