The Bethe-Schwinger cavity perturbation theory is applied to meas¬urements of the microwave dielectric constants and tensor permeabilities of small spherical samples of ferrites. For the dielectric-constant measurements, a cavity opened at a position of minimum wall currents is used. A frequency-shift method is used for measuring the real part of the dielectric constant, and a cavity-transmission method is used for measurement of the loss tangent. Circularly polarized cavity methods yield effective scalar permeabilities of which the real and the imaginary parts are measured in a manner similar to that used for the dielectric measurements. These scalar permeabilities yield sufficient information to describe completely the tensor components. Experimental data are given for a polycrystalline magnesium-manganese ferrite, to illustrate the techniques described.
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