IPC-TM-650 EN 2022 试验方法.pdf - 第467页
7.2.1.1 For the three point measurement described in 6.5.1, the calculation is 1/Q loaded = [(f 2 -f 1 )/f r ] [4] A more exact calculation can be used that does not require that the values of f 1 and f 2 be at exactly h…
6.4.1
The
computer sets the sweeper to a selected carrier
wave frequency without an AM or FM audio signal and to a
desired output power level, such as 10 dBm.
6.4.2 The same frequency is given to the synchronizer with
instructions to lock the frequency of the sweeper to the speci-
fied value.
6.4.3
The
computer checks the synchronizer for status until
the status value indicates the frequency is locked.
6.4.4
The
power meter reading is obtained by the computer.
Since it takes a finite amount of time for the power sensor to
stabilize, either a delay is used or the reading may be taken
repeatedly until consecutive readings meet a given require-
ment for stability.
6.5
Use of the Network Analyzer for Measurement of
the Specimen
An
automated network analyzer may be
used either by operating the front panel controls manually or
under computer control with suitable specialized software.
The fixture with the specimen is connected by test cables and
adapters as a device under test. Set up the instrument so the
Cartesian screen display shows the S21 parameter, the
transmission/incident power ratio, in negative dB vertical scale
units versus frequency on the horizontal scale. Select the start
and stop frequency range to sweep across the resonance
peak and at least 3 dB below the peak. Adjust the start and
stop frequency values as narrowly as possible, but still include
the resonant peak and the portions of the response curve on
both sides of it that extend 3 dB downward.
6.5.1 The
first option is to get the three points (f
r
,f
1
and
f
2
)
as
described in 6.3 or 6.4. Determine the resonant dB
r
and
frequency
f
r
values
for the highest point (maximum) on the
response curve. With manual operation, instrument program
features may be available to do this very quickly. On the
response curve to the left and right of f
r
,
locate the f
1
,d
B
1
and
f
2
,d
B
2
points
as near as possible to 3 dB below dB
r
.
These
may then be used in the calculations shown in 7.2.
6.5.2
A
second option requires a computer external to the
instrument. Collect from the network analyzer all of the f, dB
data points represented by the response curve between f
1
,
dB
1
and
f
2
,d
B
2
and
apply non-linear regression analysis tech-
niques to determine statistically values for Q
loaded
,f
r
and
dB
r
that
best fit the f
i
,d
B
i
paired
data points to the formula.
dB
i
=d
B
r
-1
0log
e
(10)
log
e
(
1+4Q
loaded
2
(f
i
/f
r
-1
)
2
)
[1]
where 10 log
e
(10)
is the constant for converting from log
e
to
dB.
This formula may be derived from formula 5 with the rea-
sonable assumption that f
r
-f
1
equals
f
2
-f
r
.
The statistically
derived values for f
r
and
Q would then be used in formulas 2
of section 7.1, formula 3 of section 7.2, and formula 6 of sec-
tion 7.3 respectively.
This has been found to fit the collected data points very well
at all regions across the entire f
1
to
f
2
range.
It is a simplified
version of the non-linear regression method for complex S21
parameters described by Vanzura
4
.
7.0
Calculations
7.1 Stripline Permittivity
Use
special care to assign the
correct n value for each resonance measured.
At resonance, the electrical length of the resonator circuit is an
integral number of half wavelengths. The effective stripline
permittivity, ε
r
,
can be calculated from the frequency of maxi-
mum transmission as follows:
ε
r
=[
nC/(2f
r
(L
+ ∆L))]
2
[2]
where
n is the number of half wavelengths along the resonant
strip of length L in mm, ∆L is the total effective increase in
length of the resonant strip due to the fringing field at the ends
of the resonant strip, C (the speed of light) is 2.9978z10
11
mm/s,
and f
r
in
Hz (or cycles/s) is the measured resonant
(maximum transmission) frequency.
The resonator ends coincide with the end edges of both the
dielectric and the ground planes. The relative fringing field at
the ends becomes extremely small. It has been the practice
with this method to ignore this fringing field and consider the
∆L value to be zero in the calculation of stripline permittivity.
7.2
Calculation of Effective Dielectric Loss Tangent
tan δ =
1/Q
unloaded
-
1/Q
c
[3]
where:
1/Q
c
is
the loss factor of the conductor
1/Q
unloaded
is
the total loss factor of the unloaded resonator
due only to the dielectric, copper, and copper-dielectric inter-
face, and does not include loss due to coupling of the probes.
7.2.1
The resonator loss factor
The
measurement of the
resonance gives a value for the loss factor of the resonator
with loading due to probe coupling (1/Q
loaded
).
IPC-TM-650
Number
2.5.5.5.1
Subject
Stripline
Test for Complex Relative Permittivity of Circuit Board
Materials to 14 GHz
Date
3/98
Revision
P
age9of11
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
7.2.1.1
For
the three point measurement described in 6.5.1,
the calculation is
1/Q
loaded
=
[(f
2
-f
1
)/f
r
]
[4]
A more exact calculation can be used that does not require
that the values of f
1
and
f
2
be
at exactly half the power level of
the maximum at resonance. This is especially suited for auto-
mated testing. The formula is
1/Q
loaded
=(
1-(f
1
/f
r
))
(10
∆1//10
-1
)
-0.5
+
[5]
((f
2
/f
r
)
-1) (10
∆2/10
-1
)
-0.5
where:
∆1
is the positive dB difference in power level from f
r
to
f
1
,
and
∆2
is the positive dB difference in power level from f
r
to
f
2
.
7.2.1.2 For
the many point measurements of the resonance
described in 6.5.2, the non-linear regression to fit the formula
1 derives the Q
loaded
value.
7.2.2
Correcting the Resonator Loss Factor for Load-
ing
The
probe gap set for about 50 dB insertion loss at
resonance is intended to make Q
loaded
approximately
equiva-
lent to Q
unloaded
.
Nevertheless, corrections in the measured
total loss value, 1/Q
loaded
are
desireable. With the assumption
that the S21 parameter with straight through connection with-
out the test fixture is at 0 dB, dBr, the insertion loss or S21
parameter in dB units at the resonant peak, is related to the
power ratio by
P
2
/P
1
=1
0
(-dBr
/10)
where
the dBr value at resonance is taken as positive. Then
the correction is
Q
unloaded
=Q
loaded
/[
1-(P
2
/P
1
)
0.5
]
or
Q
unloaded
=Q
loaded
/[
1-10
(-dBr
/20)
]
[6]
As can be seen from the following tabulation at high degrees
of insertion loss such as 50 dB errors in the straight through
connection assumption above are not as important as they
would be at lower values such as 20 or 15.
dB
60 50 40 30 20 15 10 5
Q
U
/Q
L
1.00
1.00 1.01 1.03 1.11 1.22 1.46 2.28
7.3 Calculation of 1/Q
c
The
following calculation scheme
is used to estimate the conductor loss
(5,6)
needed
for formula
3:
1/Q
c
= α
c
C/(π f
r
(ε
r
)
0.5
)
[7]
where:
α
c
=4
R
s
ε
r
Z
0
Y
/ (377
2
B)
= attenuation constant,
nepers/mm
R
s
=
0.00825 f
r
0.5
=
surface resistivity of copper, Ohms
Z
0
=
377/(4 ε
r
0.5
(C
f
+
(W/(B - T))))
= characteristic impedance of resonator, Ohm
377 = 120 π. = free space impedance, Ohm
C
f
=
(2 X log
e
(X+1)-(X-1)log
e
(X
2
-1))/ π
Y
= X+2WX
2
/
B+X
2
(1
+ T / B) log
e
[(X
+ 1) / (X - 1)] / π
X = 1/(1-T/B)
ε
r
=
relative permittivity
B = ground plane spacing, mm
W = resonator width, mm
T = resonator conductor thickness, mm
Proven data is not currently available for correcting this calcu-
lated value to account for increased conductor loss associ-
ated with roughness of the copper foil or surface treatments
for adhesion. When smooth rolled copper foil is used in Type
A specimens the estimate seems quite reliable in the 0.4 to 15
GHz range based on work done with neat (PTFE) poly(tet-
rafluoroethylene) sheet specimens
(3)
.
8.0
Report
The
report shall contain the following:
8.1
The
type of specimen: A, B, C, or D.
8.2
For
specimen type A, if not copper foil type W (wrought),
grade 5 (as rolled-wrought), bond enhancement N (none, no
stain proof), or for specimen types B, C, or D, state at least:
metal, type, grade, and bond.
8.3
The
measured length of the resonator and specimen
dielectric.
8.4
The
measured thickness of specimen cards or, if appli-
cable, of stacks.
8.5
The
center conductor width.
8.6
The
center conductor total thickness (for type C, this is
twice the cladding thickness).
IPC-TM-650
Number
2.5.5.5.1
Subject
Stripline
Test for Complex Relative Permittivity of Circuit Board
Materials to 14 GHz
Date
3/98
Revision
Page
10 of 11
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
8.7
The
temperature of the test fixture, if not in the 21°C to
23°C range.
8.8 Any
conditioning prior to measurement.
8.9
The
orientation of the resonator with respect to X or Y
axis of the specimen.
8.10
For
each resonance, show 8.10.1 through 8.10.9.
8.10.1
The
node number n.
8.10.2
The
calculated effective stripline permittivity.
8.10.3
The
calculated effective dielectric loss tangent.
8.10.4
The
resonant frequency, f
r
,
at maximum transmis-
sion.
8.10.5
The
insertion loss at resonance, dB
r
,
at maximum
transmission.
8.10.6
The
Q
loaded
.
(optional).
8.10.7
The
calculated Q
unloaded
(optional).
8.10.8
If
the three point method of 6.3, 6.4, or 6.5.1 is used,
report the frequency and dB value of the two points either side
of the peak (optional).
8.10.9
If
the non-linear regression (NLR) method of 6.5.2 is
used, report the number of data points used, NLR uncertainty
values (for f
r
,Q
loaded
,d
B
r
)
and the standard deviation of the fit
in dB units (optional).
9.0 Notes
9.1
Permittivity
The
dielectric of a stripline circuit affects
the electrical response of all the circuits printed on it. Velocity
of propagation, wavelength, and characteristic impedance all
vary with permittivity. If the permittivity varies from the design
value, the performance of such circuits is degraded.
Throughout this document, the term ‘‘permittivity’’ refers to
relative permittivity of the dielectric material, a dimensionless
ratio of the absolute permittivity of the material to that of a
vacuum.
9.2
Loss Tangent
The
attenuation and Q (figure of merit) of
stripline circuits are a function of combined copper and dielec-
tric loss. An excessively high loss tangent leads to loss in sig-
nal strength and to degraded performance of frequency selec-
tive circuits such as filters.
9.3
Dielectrics Clad with Thick Metal on One Side
This
method can be used for measurements of dielectric sub-
strates with thin foil on one side and thick cladding such as
aluminum sheet on the other by using the Type C specimen
configuration. In some cases, with very thick metal cladding it
may be necessary to use a modified part 5.1.2 (Figure 4) with
a reduced thickness dimension.
9.4
Anisotropic Materials
For
anisotropic materials, test
methods in which the electric field is not imposed on the
dielectric in a stripline configuration can give misleading values
of effective stripline permittivity and loss tangent. This test
method measures an effective stripline permittivity when the
specimen configuration is close to that of the application.
10.0
References
1. Electrical
Performance of Microwave Boards, IEEE Trans.
Components, Packaging & Manufacturing Technology,
Part B, vol. 18, no. 1, Traut, G. R, Feb. 1995.
2. The Complex Permittivity of RF Circuit Board Materials by
Resonances of a Stripline Section in the 0.2 to 15 GHZ
Range, Traut, G. Robert, Preprints of the Measurement
Science Conference 1997 January 23 & 24, Pasadena
Convention Center, Pasadena, CA
3. Complex Permittivity Over a Wide Frequency Range by
Adjustable Air Gap Probing a Stripline Resonator, Traut,
G. Robert, Proceedings of the Technical Conference, IPC
Printed Circuits Expo, March 9-13, 1997, San Jose Con-
vention Center, San Jose, CA.
4. The NIST 60-Millimeter Diameter Cylindrical Cavity Reso-
nator: Performance Evaluation for Permittivity Measure-
ments, Vanzura, E. J., Geyer, R. G. and Janezic, M.D.,
NIST Technical Note 1354, August 1993, National Insti-
tute of Standards and Technology, Boulder, CO 80303-
3328.
5. Characteristic Impedance of the Shielded-Strip Transmis-
sion Line, Cohn, S. B., IRE Trans MTT, (July 1954): pp.
52- 57.
6. Problems in Strip Transmission Lines, Cohn, S. B., IRE
Transactions MTT 3 (March 1955): pp. 119-126.
IPC-TM-650
Number
2.5.5.5.1
Subject
Stripline
Test for Complex Relative Permittivity of Circuit Board
Materials to 14 GHz
Date
3/98
Revision
Page
11 of 11
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ