Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF₂ and MgAl₂O₄ are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly.