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Ring resonator structures are widely used to characterize the frequency and temperature dependence of the relative permittivity and loss tangent of printed wiring board materials. Several theoretical models for the ring resonator structures have been presented since the first ring resonator application. In this paper, the theoretical models of the ring resonator structure are adapted for calculating the relative permittivity of low-loss and high-loss printed wiring board materials at frequency range from 250 MHz to 10.0 GHz. In addition, a review of the characterization of the loss tangent using the ring resonator is presented. The review also provides information about differences of the results due to different approximation used for conductor losses of the microstrip line. The research presented in this paper is based on an experimental research with several different microstrip and strip line ring resonator structures. The results of this study provide useful information about applying the ring resonator method for measuring the relative permittivity and loss tangent of dielectric substrates.

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Starting and reversing times of less than 40 ms, torque ripple below ten percent and operational speeds over 5000 l/min. (rpm) can be achieved with our 6/4 prototype switched reluctance motor drive. The drive efficiency approaches 80 percent but it is currently limited by high switching frquency. Peak currents of 50 A are needed in the 4.2 kW machine. Experimental results of the prototype switched reluctance machine are shown.