Stray capacitances of single-layer solenoid air-core inductors

This paper presents a method for predicting parasitic capacitances of solenoid NF inductors made of one layer of turns with circular cross sections, uniformly wound around a cylindrical nonconductive 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 the wire insulation is taken into account. An equivalent lumped parallel capacitance is derived. The method was tested by experimental measurements. The calculated and measured values were in good agreement in the considered cases. The derived expressions are useful for designing HF inductors and can also be adopted for modeling and simulation purposes.