A comparison of measurements of the permittivity
and loss angle of polymers in the frequency range
10 GHz to 90 GHz
B. L Givot1, A. P. Gregory2, B. Salski3, F. Zentis1, N. Pettit4, T. Karpisz3, P. Kopyt3
1

3M, CRAL Electromagnetics Group, St. Paul, MN 55144-1000, USA, blgivot@mmm.com
National Physical Laboratory (NPL), Engineering Materials and Electrical Science Dept., Teddington, UK,andrew.gregory@npl.co.uk
3
Warsaw Univ. of Technology (W.U.T.), Institute of Radioelectronics and Multimedia Technology, Warsaw, Poland,bsalski@ire.pw.edu.
4Pace Analytical, Scientific Professional Services, Minneapolis, MN, 55414
2Abstract—The permittivity and loss angle of disc-shaped
polymer specimens were measured by using three Split-Post
Dielectric Resonators (9.5 GHz, 25 GHz & 34 GHz), a planoconcave open resonator (36 GHz), a bi-concave open resonator(20 GHz to 50 GHz), a helical cavity (10 GHz), and two freespace Gaussian-beam transmission systems (22 – 33 GHz &60 – 90 GHz). The measured materials were PMMA,
polycarbonate, THV 500GZ fluoropolymer, and two grades ofPTFE. The work supports the need for materials for
manufacture of components for 5G applications.
Index Terms—dielectric permittivity, dielectric loss, SPDR,
open resonator, quasioptic, measurements.

I.

INTRODUCTION

This paper presents a comparison of measurements of thepermittivity and loss angle [1] of polymers by several
different methods. Such data is needed for characterizing
components use in 5G applications. Measurements weremade by using three Split-Post Dielectric Resonators(SPDRs), a Helical Cavity (HC), two open resonators (ORs),
and two Quasioptic (QO) transmission systems. Threelaboratories were involved in the comparison. Vector
Network Analyzers were used for making the measurements.
I.

SPECIMENS

Disc-shaped specimens were machined for each techniquefrom the same batch of each material. The materials were:PTFE
Two grades of the 3M™ Dyneon™ PTFE and TFM™
Modified PTFE families were used: Dyneon TF 1750 andDyneon TFM 1700.
THV 500GZ
3M™ Dyneon™ Fluoroplastic THV 500GZ, which is aterpolymer
that
contains
tetrafluoroethylene,
hexafluoropropylene and vinylidene fluoride. This material
has excellent flexibility, high optical clarity, andbondability, and can be processed at low temperatures.

PMMA and polycarbonate
The PMMA material for this study was purchased fromMcMaster-Carr. The polycarbonate material was purchasedfrom Plastics Int.
II.

METHODS

A. Split-Post Dielectric Resonators (SPDRs)
SPDRs [2] enable measurements on low loss planar
specimens to be made quickly and easily. Figure 1 shows aschematic of an SPDR. Permittivity and loss angle aredetermined from the resonant frequency and Q-factor of thequasi-TE01δ mode with and without the specimen. Each
SPDR operates at only one frequency (determined by its
dimensions). These measurements were performed at 3M.
Specimens were machined to fit the resonators: Thickness
0.5 mm (9.5 GHz), 0.3 mm (25 GHz and 34 GHz).
B. Helical Cavity (HC)Helical waveguide can be manufactured from a wire coil
set inside a resin tube. It can propagate the TE01 mode withvery low attenuation, but the degenerate TM11 mode issuppressed. The addition of metal end plates enables a cavity
to be formed (Q-factor 50,000). In the NPL design [3], apiston that is moveable by means of a micrometer is used totune the cavity (Figure 2). The empty cavity is tuned forresonance, then the specimen is inserted and the cavity isshortened to restore resonance. The permittivity and loss
angle are calculated from the change in the cavity length andmeasured Q-factors. The specimens were half a wavelength
thick in the medium of the material, in circular waveguide.
C. Bi-concave open resonator
The bi-concave Fabry-Perot OR was manufactured byEMArges Sp. z o. o., Warsaw. It allows automatic
measurement of complex permittivity of thin dielectricmaterials at multiple frequencies in a 20 – 50 GHz range
with a 1.5 GHz frequency step. The measurement of a single
sample takes about 10 minutes. The Q-factor of the empty
cavity reaches 200,000. Accuracy of the method based on aconformal transformation technique is better than 0.5% [4].
However, the largest source of uncertainty is usually due touneven thickness of the sample.
D. Plano-concave open resonatorA plano-concave Fabry-Perot OR that resonates atfrequencies in the range 30 GHz to 40 GHz was used.
Measurements were made by the fixed-frequency tuneablelength method [5]. Each specimen was measured at threemodes, to check that measurements are not affected bycoincident higher-order modes. The Q-factor of the empty
cavity is approximately 130,000. The specimens were half awavelength thick in the medium of the material.
Uncertainties were evaluated from contributions associatedwith dimensions, Q-factors, and theory.
E. Free-space transmission
Quasioptic benches manufactured by Thomas KeatingLtd., UK, for 22 GHz to 33 GHz and 60 GHz to 90 GHz
were used for measurement by transmission [6].
Calculability is improved by using corrugated horns thatradiate Gaussian beams that are almost entirely in thefundamental mode. Results were calculated with KeysightN1500A software (“Polynomial Fit Transmission Epsilon”algorithm) [7]. A two-tier calibration process is used: awaveguide calibration followed by a Gated-Reflect-Line(GRL) calibration [8].

Figure 3: Bi-concave open resonator (used at W.U.T.)

Figure 4: Plano-concave open resonator (used at NPL)

Figure 1: Split-Post Dielectric Resonator (used at 3M)

Figure 5: Free-space transmission system (used at 3M)

III.

RESULTS

The measurements are shown in Tables 1–4 and plottedin Figures 6-9.
The dielectric loss is reported in terms of the loss angle(δ), which has units of milliradians. When δ is low valued
then it is related to loss tangent (the ratio of imaginary andreal parts of permittivity) by δ ≈ tanδ ×103 milliradians. TheLynch formula [1] can be used to predict the change inpermittivity between frequency and :Figure 2: Helical cavity (used at NPL)

Figure 6: Measured permittivity and loss angle for two grades of PTFE.
Bracketed values are uncertainties at coverage factor k=2 (equivalent to approx. 95% confidence level).

Freq.

Table 1: PTFE measurements
TF1750(GHz)εʹδ milliradsεʹδ millirads

SPDR

9.5

2.042

0.2

2.051

0.2

Helical Cav.

10

2.059

0.2

2.061

0.2

SPDR

25

2.062

0.3

2.052

0.3

QO

27

2.072

0.0

2.054

0.0SPDR

34

2.055

0.3

2.044

0.3

Plano-concave OR

36

2.05(1)0.17(2)2.052(6)0.18(2)

QO

75

2.064

0.0

2.055

0.9

Bi-concave OR

36

2.045

0.2

2.046

0.2Method

TFM1700

Figure 7: THV 500GZ measurements

Figure 8: PMMA measurements

Table 2: THV 500GZ measurements

Table 3: PMMA measurements

MethodFreq. (GHz)εʹδ millirad.

MethodFreq. (GHz)εʹδ millirad.

SPDR

9.5

2.43

63

SPDR

9.5

2.66

7

Helical Cav.

10

2.44

56

SPDR

25

2.62

8

QO

27

2.3461

QO

27

2.62

7

QO

75

2.2651

SPDR

34

2.60

6Bi-concave
Open Res.

36

2.60

7QO

75

2.62

9(1)
For PTFE no significant change in εʹ is expected in themeasured range as δ is low valued. For THV 500GZ(δ≈60 milliradians at 10 GHz), εʹ is predicted to fall byapproximately 0.2 between 10 GHz and 75 GHz – which isconsistent with the results shown in Table 2.

The QO transmission methods are not expected to be able
to resolve the loss of PTFE. The graphs show that the QO
system for the 22 – 33 GHz band is able to resolve the lossfor PMMA (7 milliradians), but the 60 – 90 GHz systemcannot.

The loss of THV 500GZ was too high to permit
measurement by using open resonators. Using the Helical
Cavity, a weak resonance with the specimen in situ could be
detected – although the Q-factor was very low (reduced from50,000 to 450). The shape of the resonance was poor, which
is probably why the measured δ is lower than that obtainedwith the QO systems.

IV.

CONCLUSION

Specimens of the permittivity and loss angle of four
polymers were measured by three resonance methods, and aquasioptic transmission method. Measurements weregenerally in good agreement. The loss of PTFE is too low to
be resolved by the QO systems, but the data is useful as it
helps to establish the minimum measurable loss (which isapproximately 10 milliradians). The limiting factor is that
inserting a specimen causes shifts in the beam waist, whichchanges the mismatches and coupling (to free spaceGaussian beams) at the horns. Resonant methods arecomplementary to QO methods as they are suitable formeasuring low loss materials (typically for loss < 10milliradians).
ACKNOWLEDGMENT
The work was funded by 3M, Minnesota.

Figure 9: Polycarbonate measurements

Table 4: Polycarbonate measurements.
Bracketed values are uncertainties at coverage factor k=2(equivalent to approx. 95% confidence level)

REFERENCES[1]Method

Freq. (GHz)εʹδ millirad.

SPDR

9.5

2.80

5Helical Cav.

102.79

5SPDR

25

2.80

5QO

272.79

534

2.78

5[4]

Planoconcave
Open Res.

36

2.78(1)6.0(4)

[5]

QO

75

[2]

[3]

[6]

2.78

8[7]

R. N. Clarke (Ed.), 2003, "A Guide to the characterisation ofdielectric materials at RF and microwave Frequencies", The Instituteof Measurement and Control (IMC) and The National PhysicalLaboratory (NPL), London, ISBN 0 904457 38 9B. L. Givot, J. Krupka, and K. Derzakowski, "Split Post DielectricResonator technique for Complex Permittivity Measurements at 2025 GHz", 14th International Conference on Microwaves, Radar andWireless Communications. MIKON 2002, May, 2002.
https://doi.org/10.1109/MIKON.2002.1017876
R. J. Cook, "Microwave cavity methods" in High Frequency
Dielectric Measurement, J. Chamberlain and G. W. Chantry, Eds.
Guildford, U.K.: IPC Sci. Technol. Press, 1973, pp. 12–27
T. Karpisz, B. Salski, P. Kopyt and J. Krupka, "Measurement ofDielectrics From 20 to 50 GHz With a Fabry–Pérot Open Resonator",
IEEE Trans. Microw. Theor. Tech., Vol. 67, No. 5, 2019.
https://doi.org/10.1109/TMTT.2019.2905549
R. G. Jones, "Precise dielectric measurements at 35 GHz using an
open microwave resonator", Proc. IEE, Vol. 123, No. 4, 1976,
https://doi.org/10.1049/piee.1976.0067"Transmission /Reflection and Short-Circuit Line Permittivity
Measurements", J. Baker-Jarvis, NIST Technical Note 1341,
https://dx.doi.org/10.6028/NIST.TN.1341
P. G. Bartley and S. B. Begley, "A new technique for thedetermination of the complex permittivity and permeability ofmaterials", IEEE Instrumentation and Measurement TechnologyConference 2010, https://doi.org/10.1109/IMTC.2010.5488184
P. G. Bartley and S. B. Begley, "Improved Free-Space S-Parameter
Calibration", IEEE Instrumentation and Measurement Technology
Conference 2005, https://doi.org/10.1109/IMTC.2005.1604138