Dielectric Measurement Solutions for Materials Used in Millimeter Wave
~Keycom × Anritsu Dielectric Constant Measurement Systems~
This section introduces four methods using a VNA, the appropriate samples and measurement conditions for each
Probe method for measuring rubber and radar absorbing materials
The first is the “probe method” (Figure 4), based on the radio emission method, which is suitable for the measurement of semi-solid materials, liquids and solids. The dielectric constant can be measured by placing the probe in contact with the object. The measurement frequency range is about 10 MHz to 55 GHz, depending on the characteristics of the probe. The measurement range of the loss tangent is 0.001 to 10, making the method applicable to a wide range of measurement objects. The probe method is also used to assess the aging of rubber, concrete and other materials. This configuration is simple and portable. It can also be brought to the field for on-site measurements.
Fabry-Perot/open resonator method for film and high precision dielectric measurements
The “Fabry-Perot or open resonator method” is suitable for measuring films and sample anisotropy with high precision (Figure 5). The measurement frequency ranges from 20 MHz to 170 GHz. High accuracy measurement is possible for materials with loss tangent as small as 0.0001 to 0.05. In the open resonator method, a single resonator can cover the frequencies of 75.6, 79 and 81 GHz used by millimeter wave radar equipment and materials used as measurement targets. In addition, Anritsu’s VNA with a micro-grade automatic control mechanism allows the resonant frequency to be optimized according to a sample, improving measurement accuracy.
TM cavity resonator method for measuring powders, films, plates, liquids and low-pressure samples
The “TM cavity resonator method” is suitable for measuring powders, films, plates and liquids as well as for use in low-pressure environments (Figure 6). It is also called the “perturbation method”. The measurement frequency ranges from 200 MHz to 10 GHz and covers a lower frequency range than the open resonator method. Similar to the open resonator method, this method can work with materials with dielectric loss as low as 0.0001 to 0.05 (low dielectric loss). This method is used by many manufacturers who develop and produce powders for printed circuit boards used in electronic devices. Multiple resonances are not used for high precision measurements. Instead, one fixture is provided for each measurement frequency.
Free field method for the measurement of paints, multilayers, adhesives and liquids
The “free field method” based on the radio propagation method is suitable for the measurement of paints, multilayer materials, adhesives and liquids. The “free space method” includes the “frequency change method”, which is suitable for measuring materials with low dielectric loss, and the “S-parameter method” for measuring materials with high dielectric loss. The antenna of the free space method instrument is equipped with a radio wave lens to suppress unwanted radio wave reflections, allowing measurement in free space and eliminating the need for an anechoic chamber. This method is often used in the development of automotive-related equipment.
Anritsu’s VNA Solutions Suitable for Various Dielectric Measurements
VNA for probe method
In the probe method with a simple system configuration, a compact and lightweight 1-port model can be moved to various positions with a simple fixture and a PC to measure the dielectric constant of equipment that is actually in operation or cannot be moved from the field. Anritsu offers the MS46121B with a maximum frequency range of 6 GHz and the MS46131A with a frequency range of 8 GHz/20 GHz/43.5 GHz as 1-port models to meet various applications.
VNA for resonator method
Measurements using open and TM cavity resonators require separate outputs and inputs, making a two-port VNA ideal for these applications. For the open resonator method, which covers measurements in the relatively high frequency range, VNAs with the following measurable frequency range are available.
MS4640B 10 MHz to 40/70 GHz to 70 GHz
ME7838A/D 70 kHz to 110/125/145 GHz
The following VNAs are available for the TM cavity resonator method covering relatively low frequency bands.
MS46122B and MS46522B 1 MHz to 8/20/43.5 GHz
VNA for free field method
A 2-port VNA is also selected when performing the free field method. When implementing one of the free-field methods, the frequency-change method is suitable, which can cover a wide frequency range with the same method.
MS46522B 1 MHz to 8.5/20/43.5 GHz
ME7838A/D 70 kHz to 110/110/ 125/145 GHz
Developments beyond 5G have led to the need to measure dielectric constants up to the 300 GHz band, and by replacing the millimeter wave modules of the ME7838x series with frequency extension modules, these extremely high frequency band applications can also be addressed.
For E-band automotive radar applications, the MS46522B-08x is available for frequencies between 55 and 95 GHz and the ME7838A/D is available for the wide frequency range mentioned above.
On the other hand, for measurements in the frequency range up to 43.5 GHz, even a relatively reasonable model can be used, as long as it has a 2-port VNA. An example of this is the MS46122B. If the sample to be measured has a large dielectric loss, another high output model in the SHOCKLINE series, the MS46522B, can be selected. The MS46522B is an easy-to-use model with an ingenious design that allows the measuring cable to be easily connected to the fixture without the need for laborious maintenance.
For more details, you can access the related application note from the link below.
