Measurement of Dielectric Properties for Low-Loss Materials at Millimeter Wavelengths

Abstract

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.

Millimeter Wave Measurement of the Low-Loss Dielectric in Vacuum Electronic Devices with Reflection-Type Hemispherical Open Resonator

“…However, with the increase of the operating frequency, the material properties, such as the permittivity and the loss-tangent, are not easy to be accurately measured. The scheme of open resonator technique has been proved to be an efficient method to obtain the dielectric performance in the microwave, millimeter wave, and even terahertz regime [4][5][6][7][8][9][10][11][12][13][14][15][16]. Many advantages are demonstrated including high Q-factor (suitable for low loss-tangent test), sparser spectral density, and larger dimensions for easy manufacture.…”

“…Two different measurement routines with an open resonator of the frequency variation [6][7][8][9][10][11] and cavity-length variation techniques [16][17][18] are frequently adopted. One of the reonators is the confocal type [9][10][11]16], which is built with two symmetric concave mirrors.…”

“…One of the reonators is the confocal type [9][10][11]16], which is built with two symmetric concave mirrors. The other is the hemispherical type [6][7][8][12][13][14][15], which is built with a concave mirror and a plane one.…”

“…Since the measured S 21 is very low [6,8], a very high-resolution instrument is necessary, and the accuracy is easily affected by the background noise. In addition, vector network analyzer (VNA) [7,10], scalar network analyzer [12], spectrum analyzer [11,14,16], and power meter [9] are respectively used to construct the test system. The use of these devices not only increases the complexity and instability of the whole system but also increases the noise level.…”

Design and Measurement of a Digital Phase Locked BWO for Accurately Extracting the Quality Factors in a Biconcave Resonator System

“…The Q factors of the cavity are calculated by Lorentzian fitting or by resonance curve area method. This system can accurately measure a quality factor as high as 0.8million with an uncertainty typically less than ±1.3%, which means the system has a capability to determine the loss tangents down to the 10 −6 range [14]. …”