Secondary Resonance

Hi, does anyone know how to improve secondary resonance effects on a coil. I have a coil that is susceptable to higher frequecies (past its self resonance frequency) due to multiple secondary series resonance points?

Model the L alone and from that check the C which is causing the secondary resonance. Then tweak this C

Thanks for your reply but the secondary resonance effect of the coil is past its self resonant frequency. The series C is used to setup the primary resonance frequency. The parasitic C is a property of the coil design. Is the only alternative to re-design the coil or is it possible to lump an additional Z (i.e. an inductor or ferrite) in series with the coil to increase the effective AC resistance at these secondary series resonance points, reducing their Q and ultimately, their unwanted interference?

You did not got my point. remove the C which is causing the primary resonance. then you have L only.
Now measure S para for that.
Have a topology that matches with the measured data. this procedure is called modeling a component.
Now if you observe this inductor model there will be a capacitor.
I am talking about this Capacitor and proceed the same way as explained before

Understand your point. If the secondary resonance caused by the parallel Cp is causing you problems that is probably because Cp is of the same order of magnitude than the series capacitance Cs.

Make an estimate of Cp as explained before. Or you can estimate Cp also from the self-resonant frequency explained in the datasheet also.

A rule of thumb is that Cp should preferrably be 10x bigger then Cs. If this is not the case select a smaller L (=smaller Cp) and bigger Cs. Of course loaded Q will decrease.

Thanks for your reply. However, you mention making Cp 10 times larger than Cs. In my application, I have purposfully designed the coil to have a low self resonance frequency. However, my query is, can I effect the coils susceptability/immunity to frequencies past its self resonant frequency? I can see from an impedance analyser that the coil has multiple secondary series and parallel resonant points up to 2GHz (SRF <50MHz). I understand the coils behaviour up to its SRF but past its self resonance it is effectively a capacitor. I intend to model the high frequency behaviour of the coil in the coming weeks with CST but I am struggling to understand the concept of how these higher frequency resonant points are being setup and how I can influence them while keeping the and primary self (parallel) resonant point at the same frequency. For example, is it reasonable to think that if I have a spiral coil with 100 turns, at some higher frequency beyond its SRF, this coil looks electrically like a single turn because Cp between the turns has become so large that the turns are effectively shorted at this frequency?

Thanks again for taking the time to respond, your input is appretiated.