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Concept for Equivalent Dielectric Constant of Planar Transmission Lines on Anisotropic Substrates

Authors:
Plamen Dankov at Sofia University "St. Kliment Ohridski"
Plamen Dankov
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Abstract and Figures

Dielectric anisotropy of the modern reinforced substrates for RF and MW electronics and how the main substrates’ producers consider this issue; Methods for characterization of substrate anisotropy; “two-resonator method” and data for same typical RF and MW substrates; Concept for equivalent dielectric parameters of the anisotropic microwave substrate to transform it into isotropic equivalent and methods for their determination; Determination of the equivalent dielectric parameters for different planar transmission lines – a comparison How the modern 3D simulators can cope with the dielectric anisotropy? How to solve the problems with the different equivalent parameters, which are suitable for accurate 3D design of anisotropic planar structures in the frequency ranges allocated to the future 5G standard? Conclusions and future work
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Concept for Equivalent
Dielectric Constant of Planar
Transmission Lines on
Anisotropic Substrates
by Plamen Dankov
London, October 2016
Faculty of Physics, Sofia University “St. Kliment Ohridski”
46th European Microwave Conference (EuMC)
London, 4–6 October 2016
1
London, October 2016
Known fact: Most of the modern microwave substrates
are reinforced and therefore – anisotropic!
2
h
t
t
'r , tan
Metallization
Not metallized substrates
• Reinforcing woven fiberglass: glass fibers or filaments drawn out from the same material (self reinforcing)
• Resin fillers: organic or nonorganic substances, powders, polymers, etc.
Planar structures on the same substrates
London, October 2016
Dielectric anisotropy
3
“Crystalline” anisotropy: mono- or poly-crystalline
materials (optical glasses, microwave ceramics, LTCC, liquid
crystals); these materials are homogeneous, but anisotropic
due to their crystalline structure; this anisotropy is usually
relatively strong;
Magnetic or electric “gyrotropy”: this is the
original concept for the material anisotropy (ferrites, gaseous or
solid-state plasmas, ferroelectric materials and films; all in external
magnetic or electric fields; so-called “induced anisotropy”),
tensor form of the permittivity and permeability, controlled
by external dc biasing field;
“Artificial” anisotropy: engineered meta-materials
and “band-gap” materials with controllable dielectric
constant in different directions; composite and multi-layer
meta-substrates;
Dielectric uniaxial anisotropy of reinforced
substrates (commercial engineered reinforced substrates
for the modern RF and microwave electronics) ; see
 
'00
0'0
00'
'
ˆ||
||
r
 
tan00
0tan0
00tan
ˆ
tan ||
||
Parameters that characterize dielectric anisotropy:
A = 2(
'||
')/(
'|| +
') or simple A =
'||/
'
Atan = 2(tan
|| tan
)/(tan
|| + tan
) or simple
Atan = tan
||/tan
'||, tan
||
Oy
Oz
Ox
', tan
London, October 2016
Outline
Dielectric anisotropy of the modern reinforced substrates for RF and MW
electronics and how the main substrates’ producers consider this issue;
Methods for characterization of substrate anisotropy; “two-resonator
method” and data for same typical RF and MW substrates;
Concept for equivalent dielectric parameters of the anisotropic microwave
substrate to transform it into isotropic equivalent and methods for their
determination;
Determination of the equivalent dielectric parameters for different planar
transmission lines – a comparison
How the modern 3D simulators can cope with the dielectric anisotropy?
How to solve the problems with the different equivalent parameters, which
are suitable for accurate 3D design of anisotropic planar structures in the
frequency ranges allocated to the future 5G standard?
Conclusions and future work
4
London, October 2016
Typical substrate parameters presented in commercial web sites (1)
Cu foil parameters Dielectric parameters
5
Thermal parameters
Standard dielectric
thickness
London, October 2016
6
Typical substrate parameters presented in commercial web sites (2)
London, October 2016
7
Typical substrate parameters presented in commercial web sites (3)
London, October 2016
Substrate dielectric constant – why so many different parameters?
8
•2002 – we maybe were the first researchers, which pointed, named and measured the dielectric
anisotropy of reinforced substrates
•2004 – we published full datasheets for dielectric anisotropy of many commercial substrates and
started to introduce a new parameter – “equivalent dielectric constant”
•2004 -2016 – we accumulated big database for dielectric anisotropy and equivalent dielectric
constant for more than 100 variants of commercial substrates.
•2005 – Taconic Headquarters Ltd. was the first company, which officially shared information for the
dielectric anisotropy of TLY-5A (measured by Bereskin’s method)
•After that Rogers Corp started to give two values of its dielectric substrates: process and design values
•2012/16 – Rogers Corp. shared information about the measured anisotropy of some of its products
•2013/15 – Isola Group Ltd. started to discuss and to solve the problems with substrate anisotropy,
especially at higher frequencies and shared information for the equivalent dielectric constant.
London, October 2016
Measurement of dielectric anisotropy
9
This test method gives near-to-
perpendicular parameters of SUT
according to the substrate surface:
Dielectric constant ~
'
Dissipation factor ~ tan
Substrate
under test
(SUT)
Wide
stripline
resonator
pressure
E field pattern
A possibility to measure the parallel dielectric
parameters – but a new substrate has to prepared
by laminated pieces from the same material,
from which have to be cut longitudinal sections
and to manufacture new stripline resonator. All
this makes the method very difficult for
technical realization and rather inconvenient
SUT
IPC TM-650 2.5.5.5 Clamped Stripline Resonator Test Method Modified IPC TM-650 :
Bereskin’s method
London, October 2016
Measurement of dielectric anisotropy (2)
10
Rectangular waveguide resonators with samples Rectangular Resonator: perturbation method
London, October 2016
Measurement of dielectric anisotropy (2)
11
Side-Coupled Microstrip RA-resonator; odd/even modes) SIW Resonator Method
London, October 2016
Two-resonator method
12
Source: Plamen I. Dankov, "Two-Resonator Method for
Measurement of Dielectric Anisotropy in Multi-Layer
Samples”, IEEE Trans. on Microwave Theory and Tech.,
MTT-54, pp. 1534-1544, April 2006
TE011-mode resonator R1:
parallel parameters:
‘//||, tan
||
( 1.5 %; 5 %)
TM010-mode resonator R2:
perpendicular parameters:
', tan
( 5 %; 15 %)
sample
H2
D2
D1
R2
H1
E field
R1
We developed (2004-2011) an authorship resonance method for determination
of the dielectric anisotropy of microwave substrates with good enough
accuracy and applicability to single-layer and multi-layer substrates.
London, October 2016
Five cylindrical resonators “cover” a frequency range 6-38 GHz
13
Split cylinders
Re-entrant resonators
Cylinders Split-coaxial cylinders
London, October 2016
Data for dielectric anisotropy of two typical substrates (1)
14
1st typical commercial substrate with
relatively small anisotropy denoted as
“Substrate 3.00” with reference
(catalogue) value Dk = 3.00
2nd typical commercial substrate with
relatively moderate anisotropy denoted
as “Substrate 3.38” with reference
(catalogue) value Dk = 3.38
London, October 2016
15
Data for dielectric anisotropy of two typical substrates (2)
Dielectric anisotropy according to the
substrate thickness
London, October 2016
How to use the results for substrate anisotropy in the modern
3D design of planar structures?
16
I. To neglect the dielectric
anisotropy and to use the
reference (catalogue) value
for dielectric constant,
obtained by IPC TM-650
2.5.5.5 method (“process”
or “technological” value):
'sim
'
III. To use the anisotropic
option with data for the
actual measured substrate
anisotropy:
'// 0 0
'sim = 0
'// 0
0 0
'
II. To use an equivalent
dielectric constant of the
equivalent isotropic
substrate (“design” value in
the case of microstrip line):
'sim =
'eq = a
'// + b
'
London, October 2016
Idea for this approach: to replace the anisotropic substrate with
an isotropic equivalent substrate with equivalent dielectric
constant
'eq and equivalent dielectric loss tangent tan
, eq
17
'eq = a.
'// + b.
' ;
tan
, eq = c.tan
// + d.tan
a, b, c, d – appropriate constants; we
suppose that they depend on the
different type of planar structure
Example: Our first results from 2002 for a
typical substrate RO4003, valid in the
frequency range 1-40 GHz
'// ~ 3.67;
' ~ 3.37 (anisotropy)
'eq = 3.53 0.02 (equivalent value for MSL)
'r = 3.38 (reference value IPC TM-650 2.5.5.5)
London, October 2016
18
1) Differential phase-length method (1-40
GHz): four planar lines with different length
GCPWG
CPWG MSL
'eq
Substrate 3.00
tan
, eq
Substrate 3.00
Methods for determination of equivalent parameters (1)
London, October 2016
19
GCPWG
2) Set of 2-3 linear resonators with
different length (1-40 GHz)
CPWG
MSL
CMSL
PS
fres
'eq Qres tan
, eq
Methods for determination of equivalent parameters (2)
Substrate 3.0 20/10 mils
London, October 2016
20
GCPWG
3) Ring resonators (1-40
GHz)
CPWG
MSL
SlL PS
Methods for determination of equivalent parameters (3)
London, October 2016
21
Test plates for different planar lines
London, October 2016
Determination of effective dielectric constant of planar lines (1)
22
A simple modification of the known reference method of
clamped stripline resonators, but now – clamped
microstrip resonators (“quasi-IPC TM 650” method)
London, October 2016
23
Determination of effective dielectric constant of planar lines (2)
London, October 2016
24
Determination of effective dielectric constant of planar lines (3)
London, October 2016
Determination of the equivalent parameters of planar lines (1)
25
1) Widespread transmission-line (TRL) calculators;
2) 3-D simulations of appropriate well-constructed
3-D models of different planar transmission lines
3) Analytical closed-form models; CAD models for
some transmission lines, if exist
London, October 2016
26
Determination of the equivalent parameters of planar lines (3)
London, October 2016
Equivalent parameters of different planar lines – final results
27
London, October 2016
Three different equivalent values for 3 groups of planar lines?
28
Three different groups of values for the equivalent dielectric
constants could be acceptable for incorporation in the modern
3D-design of planar structures:
1) Microstrip value:
eq =
eq_MSL (or so-called “design Dk”) for
planar lines with mixed distribution of parallel and
perpendicular electric fields suitable for: microstrip lines,
coupled microstrip lines (for even and odd modes); paired
(parallel) strips, grounded coplanar waveguides, and similar
planar structures;
2) Stripline value:
eq =
perp_sub (reference, “process Dk”,
obtained by the known IPC-TM-650 2.5.5.5 clamped stripline
test method) for planar lines with predominant perpendicular
electric fields: striplines, substrate integrated waveguides
SIW, wide parallel-plate structures and similar planar lines.
3) Coplanar value:
eq =
eq_CPWG (new parameter “coplanar
design Dk”) for planar lines with predominant parallel
electric fields: coplanar and slot-based transmission lines,
mainly coplanar waveguides, slot lines, fin-lines, etc. (for slot
lines the value
eq =
par_sub is most suitable);
This is our concept for utilization of equivalent substrates
for better RF and MW 3D design of planar structures on
anisotropic substrates.
London, October 2016
29
Conclusions
•Its time to include the information for the measured dielectric
anisotropy in the reference data for each commercial substrate! It
means to select an acceptable method for accurate and fast
determination of this anisotropy.
•The equivalent parameters of each commercial substrate could be
used for replacement of the anisotropic substrate into a isotropic
equivalent to be used in the modern 3D design;
•At least three different equivalent dielectric constants should be
offered to the RF and MW designers for accurate design of different
planar structures: 1) near-to-perpendicular value (for SL and SIW); 2)
true equivalent (design) value (for microstrip-like structures) and 3)
near-to-parallel value (for coplanar and slot-based structures);
•A lot of future work for verification of the anisotropic option of
modern 3D simulators and to offer new fast methods for
determination of the equivalent parameters!
London, October 2016
Future work (1)
30
How the modern 3D simulator cope
with the substrate anisotropy?
London, October 2016
31
How to predict the equivalent parameters on
the base of near-field distribution in different
planar lines?
Future work (2)
London, October 2016
32
Determination of the parallel and perpendicular E-fields in different planar lines’ zones
Future work (2)
London, October 2016
33
How to predict the equivalent parameters on the base of near-field distribution in
different planar lines?
Future work (2)
Particular case: MSL
London, October 2016
34
A new method for direct determination of the
equivalent parameters on the base of covered MSL
and other planar lines (with dielectric overlay under
pressure)
Future work (3)
Thank you for the attention!
35
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... Both extracted curves for ε eq_M S L and tanδ ε_eq_M S L , lies between the measured curves ε par , ε perp and tanδ ε_ par , tanδ ε_perp . This is a typical fact for most of the anisotropic materials [42] and shows that the obtained results are in full compliance. The other important fact is the observed weak but measurable frequency dependence of the dielectric constants: ε par ∼ 2.8-2.7; ...
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... The real part ε eq 0 is the equivalent dielectric constant whereas the imaginary part ɛ eq 00 indicates the equivalent loss factor. Both the real and imaginary parts compose of two anisotropic components: perpendicular and parallel components as given by 32,33 ε eq = ε 0 eq −jε 00 eq = ...
... 29 In addition, most commercial DSs suffered from the dielectric anisotropy due to the layer reinforcement using different nonisotropic substances. The anisotropy substrate can be characterized by two pairs of parameters for obtaining the equivalent dielectric constant and equivalent dissipation factor: (ε || 0 tanδ || ) -parallel dielectric parameters, and (ε ┴ 0 , tanδ ┴ ) -perpendicular dielectric parameters as given by, 32,33 ...
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... The real part ε eq 0 is the equivalent dielectric constant whereas the imaginary part ɛ eq 00 indicates the equivalent loss factor. Both the real and imaginary parts compose of two anisotropic components: perpendicular and parallel components as given by 32,33 ε eq = ε 0 eq −jε 00 eq = ...
... 29 In addition, most commercial DSs suffered from the dielectric anisotropy due to the layer reinforcement using different nonisotropic substances. The anisotropy substrate can be characterized by two pairs of parameters for obtaining the equivalent dielectric constant and equivalent dissipation factor: (ε || 0 tanδ || ) -parallel dielectric parameters, and (ε ┴ 0 , tanδ ┴ ) -perpendicular dielectric parameters as given by, 32,33 ...
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Article
  • Feb 2008
We present a measurement method to characterize low-loss engineered materials and natural uniaxial dielectrics. Our approach employs a rectangular cavity coupled with tailored finite-element simulations to accurately determine the permittivity tensors and loss tangents of material assemblies. Although similar approaches for natural crystals have been reported, this is the first time this method is adapted to engineered metamaterials. Loss-tangent measurements with an accuracy of 4-5 significant digits can be achieved by this simple and effective measurement approach. To demonstrate the method, we characterize a layered barium titanate-alumina stack and show that low-loss engineered crystals can be achieved via a proper choice of a bonding agent.
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