Characterization and concept for optimization of planar spiral high power high frequency coils

Parasitic effects lower the self-resonant frequency of a coil and therefore limit its usable frequency range. In this paper a method is presented to substantially expand the usable frequency range of high current rated inductors. The basic idea of the method is to control the resonant frequencies of a coil by placing a gap between groups of windings and to connect a resistor network in parallel. The concept is investigated at a planar spiral topology of a coil. An appropriate equivalent circuit is developed and calculated. Systematic investigations of the coil allow stating approximations about inductance, the parasitic capacitance and resonant frequency. The concept is finally approved by real measurements on a prototype coil. In a last step the proposed HF-coil is assembled to a prototype filter.