Abstract-A system has been developed for measuring the complex permittivity of low loss materials at frequencies from 500 MHz to 7 GHz and over a temperature range up to 1500 • C using stripline resonator cavity method. Details of the design and fabrication of the cavity were discussed. Particular features related to high-temperature operation were described. An improved resonance method at high temperature for determining complex dielectric properties of low-loss materials was developed. The calculation process was given by a physical model of the stripline resonator cavity at high temperature. The paper brought forward the method of segmentation calculation according to the temperature changes over the cavity, which matched the actual situation of high temperature measurements. We have verified the proposed method from measurements of some typical samples with the available reference data in the literature.

We describe here a system for accurate measurement of the dielectric properties of very low-loss materials in the 130 to 170 GHz frequency range. This system utilizes an open resonator with a quality factor ∼1×10 6 . Resonance curves for this resonator are acquired with a commercial spectrum analyzer equipped with an external millimeter-wave harmonic mixer. The excitation source is a backward-wave oscillator locked to the spectrum analyzer local oscillator via a digital phase-locked loop. This system permits rapid and accurate measurement of resonance curve line widths, permitting determination of loss tangents down to the 10 -6 range. Results are reported for silicon carbide (SiC), CVD diamond, sapphire, and quartz.

The combination of a D-Band phase-locked backward-wave oscillator (BWO) with a spectrum analyzer for measurement of permittivity and low loss-tangent is presented. For measuring low loss tangent material, such as CVD diamond and high purity semi-insulating ( ) 4SiC, at millimeter wave ranges, it is necessary to precisely measure an increase of a few kHz in a line-width of 200 kHz. We describe a phase-locked loop with frequency conversion that combines a BWO source and a microwave spectrum analyzer to obtain line-width measurements with less than 2 kHz (less than 1%) standard deviation in D-Band millimeter wave.Index Terms-Backward-wave oscillators (BWOs), frequency conversion, millimeter wave, phase-locked loop (PLL).

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