Stray capacitances of single-layer air-core inductors for high-frequency applications

A method for predicting stray capacitances of HF inductors dependent on their geometry is presented. The analysis is performed for inductors made of one layer of turns with circular and rectangular cross-sections. The wire is uniformly wound around a cylindrical nonferromagnetic core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence of insulating coatings of the wire is also taken into account. An overall equivalent stray capacitance is derived according to the typical HF equivalent lumped parameter circuit of inductors. The method was tested with experimental measurements and the accuracy of the results was good in most cases. The derived expressions are useful for designing of HF inductors and can be also used for simulation purposes.