IPC-TM-650 EN 2022 试验方法.pdf - 第439页
Cartesian screen display shows the S21 parameter and 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 …
be
taken to assure that power is continuously supplied to this
unit to avoid a longer warm-up time. Other equipment using
vacuum tube devices will require a longer warm-up time as
specified in the manufacturer’s literature.
The temperature of the test fixture shall be in the range of
22°C to 24°C, unless otherwise specified. If this standard
temperature is to be used and the temperature of the fixture
is to be controlled by the ambient conditions in the testing
laboratory, then the laboratory shall be maintained at 22°C to
24°C and the fixture shall be stored in the laboratory for at
least 24 hours prior to use.
If non-standard temperature is specified and the fixture of 4.1
is used with the temperature control apparatus described in
4.2, then the rest of this paragraph applies. Prior to making
electrical measurements, the circulator is started and adjusted
to within 1°C of the desired test temperature. The time
required for stabilization depends on the specific temperature
control apparatus in use, the size of the circulation bath tank,
and the temperature selected. Additional stabilization time will
be required for each specimen to come to the set temperature
after it has been clamped in the fixture.
The test fixture containing the test specimens shall be placed
in the clamping fixture and the specified force of 4.45 ± 0.22
kN is applied through the calibrated force gauge to the 1290
mm
2
area
centered directly over the resonant circuit as shown
in the assembly of Figure 12, Figure 13, or Figure 15.
6.2
Manual Measurement of the Specimen
The
follow-
ing procedure is applicable where equipment as described in
4.1 is available. The equipment of 4.2 could also be operated
manually. The stripline resonator formed by the fixture pattern
card and ground planes with the specimen cards inserted is
referred to as a cavity. The sweep oscillator is referred to here
as the sweeper.
6.2.1
Determination of Cavity Resonant Frequency
The
resonant
frequency of the circuit shall be found by scanning
the sweeper over the expected transmission range of the test
resonator. The sweeper shall be precisely adjusted to the fre-
quency that produces a maximum reading of the SWR Meter
No. 1. The frequency meter shall then be adjusted for a mini-
mum reading of the SWR Meter No. 2. Record the resonant
frequency. The input selector of the SWR Meter No. 1 should
be set for low impedance input for proper square law detec-
tion.
6.2.2
Determination of Cavity Half-Power Points
With
the
incident signal having been set to maximum resonator
transmission, adjust the gain of the SWR Meter No. 1 until the
meter reads 0 dB. The frequency of the sweeper shall then be
adjusted to give 3 dB readings both above and below the
maximum transmission frequency. Measure each frequency
with the frequency meter and record the results:
• f1: above the maximum transmission frequency
• f2: below the maximum transmission frequency
6.3
Automated Measurement of the Specimen
For
an
automated system to be used in performing the measure-
ment, computer software is needed that will collect paired
values of frequency and transmitted power. From this data,
the frequency for maximum power transmission and the fre-
quencies of the half power points are determined. The com-
puter program may optionally include computation of permit-
tivity and loss tangent as described in 7.0. Results and
collected data may be displayed on the screen, stored in a
disk file, sent to a printer, or any combination of these.
In one possible mode of operation with the equipment
described in 4.2, the following sequence of steps is performed
as many times as necessary to get enough data to complete
the test procedure. The computer is designated as the con-
troller on the GPIB.
6.3.1
The
computer sets the sweeper to a selected carrier
wave frequency without an AM or FM audio signal to a desired
output power level, such as 10 dBm.
6.3.2
The
same frequency is given to the synchronizer with
instructions to lock the frequency of the sweeper to the speci-
fied value.
6.3.3
The
computer checks the synchronizer for status until
the status value drops to zero, indicating the frequency is
locked.
6.3.4
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.
6.4
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
IPC-TM-650
Number
2.5.5.5
Subject
Stripline
Test for Permittivity and Loss Tangent (Dielectric Constant
and Dissipation Factor) at X-Band
Date
3/98
Revision
C
P
age6of25
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
Cartesian
screen display shows the S21 parameter and 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 downward 3 dB.
6.4.1
The
first option is to get the three points (f
r
,f
1
,
and f
2
)
as
described in 6.2 and 6.3. 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 are 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.
6.4.2
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 statistically determine values for Q, 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
-
A log
e
(
1+4Q
2
((f
i
/f
r
-1
)
2
)
where
A=1
0log
e
(10)
= constant for converting from log
e
to
dB
This formula may be derived from combining equation 4 and
equation 6 as corrected in 7.2, with the reasonable assump-
tion that f
r
-f
1
equals
f
2
-f
r
.
The statistically derived values for
f
r
and
Q would then be used in equation 2 of 7.1 and equa-
tion 4 of 7.2 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
5
.
7.0
Calculations
7.1 Stripline Permittivity
At
resonance, the electrical
length of the resonator circuit is an integral number of half
wavelengths. The effective stripline permittivity, ε
r
,
can be cal-
culated from the frequency of maximum transmission as fol-
lows:
ε
r
=[
nC/(2f
r
(L
+ ∆L))]
2
[1]
Where
n is the number of half wavelengths along the resonant
strip of length L, ∆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 3.000z10
11
mm/s, and
f
r
is
the measured resonant (maximum transmission) fre-
quency.
The more exact value for C of 2.9978z10
11
mm/s
would give a
lower permittivity value, differing for example by 0.003 for 2.5
permittivity material. This method does not use the more exact
value to avoid confusion with specifications for materials and
proven component designs based on older versions of this
method where 3.000z10
11
has
been in use.
For example, for a specified 38.1 mm long resonator, the
parameters at X-band aren=4,L=38.1 mm. For a given
material with ∆L = 1.397 mm, the formula for ε
r
becomes:
ε
r
=
2.30764z10
20
/f
r
2
[2]
7.1.1
Determination of L
∆L,
a correction for the fringing
capacitance at the ends of the resonator element, is affected
by the value of the ground plane spacing and the degree of
anisotropy of permittivity of the material being tested. The
degree of anisotropy is affected by the amount and orientation
of fiber and the difference between permittivity of fiber and
matrix polymer. Because of this, a ∆L value for use with a
particular type of material must be determined experimentally
by the following procedure.
7.1.1.1
Prepare
a series of resonator circuit cards having
patterns in which only the resonator element length is varied
to provide n values of 1, 2, 3, and 4 at close to the same fre-
quency. For example, lengths of 9.5 mm, 19.0 mm, 28.6 mm,
and 38.1 mm may be used.
7.1.1.2
For
each of at least three sets of typical specimen
pairs of the material to be measured, measurements of f
r
are
obtained
at each L value. Plot L f
r
/n
on the Y axis versus f
r
/n
on
the X axis or preferably use a numeric linear regression
analysis procedure to determine the slope of the least squares
fit through the four data points. The slope is equal to the
negative value of ∆L.
7.1.1.3
The ∆L
values for each of the specimen pairs may
then be averaged to provide a suitable working ∆L value. For
a given material type, a ∆L value should be agreed upon as
standard for testing to a specification.
7.1.2
Determination of Effect of Specimen Thickness on
L
The ∆L
correction for end fringing capacitance will vary
IPC-TM-650
Number
2.5.5.5
Subject
Stripline
Test for Permittivity and Loss Tangent (Dielectric Constant
and Dissipation Factor) at X-Band
Date
3/98
Revision
C
P
age7of25
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
with
specimen thickness, increasing as specimen thickness
increases. Ignoring this effect by use of a fixed ∆L value for
calculating test results will bias the permittivity values upward
for thicker specimens, downward for thinner ones. For low
permittivity materials where the resonator is longer, this bias is
quite small and only of interest for close tolerance applica-
tions. For high permittivity materials, the smaller resonator
length makes this correction more important.
There are two ways in which this thickness effect may be
handled: by an empirical determination of ∆L for various thick-
nesses or by assuming a proportionality to the published pre-
diction of ∆L
(4)
.
7.1.2.1
For
the empirical method, use the 7.1.1 procedure
to obtain ∆L with specimens at extremes of thickness variation
expected in day to day testing. Use numerical linear regres-
sion of the collected ∆L-specimen thickness data pairs to
derive a linear formula of the form
∆L=B0+B
1
(thickness)
Specification
values for B
0
and
B
1
for
a given material must be
agreed upon for a particular material type.
7.1.2.2
A ∆L
correction factor can be derived for a given
material type in a range of permittivity values by determining
for specimens of known thickness the ratio of ∆L derived
according to 7.1.1 to that predicted by equation 3 when R=1.
An average of ratios so determined must be agreed upon as
the specified correction factor for the formula. From this, ∆Lis
calculated by:
∆L= R (K
2
+2KW
)/(2K+W) [3]
where
R = the average ratio of observed to predicted ∆L
K = B log
e
(
2)/pi
= 0.2206356 B
W = width of resonator in mm
B = 2 (specimen thickness) + (test pattern card thickness)
= total ground plane spacing in mm
7.2
Calculation of Effective Dielectric Loss Tangent
A
value
for loss tangent for the dielectric is obtained by subtract-
ing the appropriate conductor loss value, 1/Q
c
,
in Table 1
from the total loss value, 1/Q, as shown
tan δ = 1/Q - 1/Q
c
[4]
or
tan δ =[
(f
1
-f
2
)/f
r
] - 1/Q
c
[5]
where
1/Q or (f
1
-f
2
)/f
r
is the total loss due to the dielectric, copper,
and copper-dielectric interface.
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
tan δ = (1-(f
1
/f
r
))
(10
(dB
1
/
10
)-1
)
-0.5
+
((
f
2
/f
r
)-1
)(10
(dB
2
/
10)
-1
)
-0.5
-
(1/Q
c
)
[6]
dB
1
is
the dB below the peak power level at f
1
and
dB
2
is
the dB below the peak power level at f
2
7.2.1
Calculation of 1/Q
c
The
following calculation scheme is used
(1)
1/Q
c
= α
c
C/(π f 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
0.5
=
surface resistivity of copper, Ohm
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 = B/(B-T)
ε
r
=
nominal permittivity
B = ground plane spacing, mm
C = 299.796 mm/ns = speed of light
f = nominal resonant frequency, GHz
IPC-TM-650
Number
2.5.5.5
Subject
Stripline
Test for Permittivity and Loss Tangent (Dielectric Constant
and Dissipation Factor) at X-Band
Date
3/98
Revision
C
P
age8of25
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ