 |
Description  |
|
|
TECHNICAL FIELD
The present invention relates to the field of noise parameter testing. More
specifically, the present invention relates to determining the noise
parameters of a device under test (DUT) by measuring simultaneously the
DUT's noise power within different, closely spaced, narrow frequency
ranges. The invention also relates to one-port tuners for use in noise
power measurements within different frequency ranges.
BACKGROUND OF THE INVENTION
When a signal passes through a network, the network adds noise to the
signal. Because noise limits the amount of information a signal having a
given power can contain, noise minimization is often desired in limited
signal power situations, for example, satellite communications.
A standard measure for the amount of noise added to a signal by a two-port
network is termed "noise factor" ("noise figure" when measured in
decibels), and is defined in "IRE Standards on Methods of Measuring Noise
in Linear Twoports, 1959," 59 IRE 20. Sl, Proc. IRE, vol. 48, pp. 60-68,
January 1960, reprinted in Low-Noise Microwave Transistor & Amplifiers
IEEE Press, 1981:
"The noise factor, at a specified input frequency, is defined as the
ratio of (1) the total noise power per unit bandwidth at a corresponding
output frequency available at the output port when the noise temperature
of the input termination is standard (290 K) to (2) that portion of (1)
engendered at the input frequency by the input termination."
The noise factor F of a two-port network is a function of the source
admittance Y.sub.s and varies according to the equation
##EQU1##
F.sub.0 is the network's "optimum noise factor" and is the minimum noise
factor which may be achieved by setting the source admittance Y.sub.s to
an optimum admittance Y.sub.0. R.sub.n is a parameter having the units of
resistance, and G.sub.s is the real or conductance component of the
complex source admittance Y.sub.s, the imaginary component B.sub.s being
susceptance. Since Y.sub.s =G.sub.s +jB.sub.s and Y.sub.0 =G.sub.0
+jB.sub.0, equation (1) may be rewritten as
##EQU2##
A network's noise performance at a given frequency can be described by
specifying its four noise parameters F.sub.0, G.sub.0, B.sub.0, and
R.sub.n. These four parameters are independent of the source and load
terminations. A graph of noise factor F on the rectangular source
admittance plane is shown in FIG. 1.
Noise factor F also may be graphed on the complex reflective coefficient
plane, i.e., a Smith chart, as described by H. Fukui in "Available Power
Gain, Noise Figure, and Noise Measure of Two-Ports and Their Graphical
Representation," IEEE Trans. Circuit Theory, vol. CT-13, pp. 137-142, June
1966, and also reprinted in Low-Noise Microwave Transistors & Amplifiers.
A Smith chart having circles representing source reflection coefficients
which yield constant noise figures for a hypothetical DUT is shown in FIG.
2.
A DUT's noise parameters for a given frequency can be calculated from the
DUT's noise factor at the same frequency for four different source
admittances. Due to inevitable errors in measurement and possible singular
solutions, preferably more than four measurements are made and the noise
parameters are calculated using a fitting method, one method being
described by Richard Q. Lane in "The Determination of Device Noise
Parameters," Proc. IEEE, vol. 57, pp. 1461-1462, August 1969 which is also
reprinted in Low-Noise Microwave Transistor & Amplifiers.
To assure accurate calculation of the noise parameters, and especially the
minimum noise factor F.sub.0, some noise factor measurements should be
taken which are not on the steep slope of the surface F shown in FIG. 1.
To ensure this, the noise power should be measured for many different
source admittances, or source reflection coefficients, such that the
measurement points permeate the entire Smith chart. Such a pattern of
measurement points on a Smith chart will be called hereinafter a
"constellation."
In Leake, U.S. Pat. No. 4,502,208 an electrically controllable tuner is
described. However, the tuner does not provide a constellation which fills
the Smith chart; the points are concentrated in the center. Vahe Adamian
and Arthur Uhlir, Jr. describe using off-set short circuits as the source
admittance. ("Simplified Noise Evaluation of Microwave Receivers," IEEE
Transactions on Instrumentation and Measurement, Vol. IM-33, No. 2, June
1984.) Unfortunately, such tuners only allow constellations with points on
the edge of the Smith chart.
Larock and Meys describe a method of changing the source admittance in
noise measurements by changing the measurement frequency a relatively
small amount. ("Automatic Noise Temperature Measurement Through Frequency
Variation," IEEE Transactions on Microwave Theory and Techniques, Vol.
MTT-30, No. 8, August 1982.) A slight change in measurement frequency
causes the measurement source admittance points to move in an arc around
the center point of a Smith chart. With relatively small changes in
measurement frequency, a measurement source admittance point may be moved
full circle around the Smith chart.
Since noise parameters vary according to signal frequency, a complete noise
parameter analysis requires multiple measurements of noise factor at
multiple frequencies. Since noise is a random event, an accurate
measurement of its power requires increasing time for decreasing bandwidth
of measurement. Thus, accurate measurements of noise parameters can
require significant time.
What is needed, then, is an improved method and apparatus for accurately
measuring and calculating noise parameters of a two-port network while
decreasing the time required for the measurements. Also needed is a method
and apparatus for providing a broad constellation of source admittances,
yielding more useful measurements of noise factor from which to calculate
a DUT's noise parameters.
SUMMARY OF THE INVENTION
The present invention provides apparatus and means for simultaneously
measuring a two-port device under test's (DUT's) noise power within
different frequency ranges. The different frequency ranges are
sufficiently close to a central frequency such that the DUT's noise
performance is substantially the same as at the central frequency; slight
frequency-dependent noise factor changes may be calculated and eliminated
or ignored. The Smith chart representation of noise figure shown in FIG. 3
more clearly shows the frequency relationship between the source
admittance and the noise factor. Since a DUT's noise factor does not vary
rapidly with small changes in measurement frequency, the measurement
frequency may be varied slight to alter the source admittance seen by the
DUT's input port. For example, assume the source termination is a delay
line having a length 5 nanoseconds and the measurement is 10 GHz. An
exemplary source admittance is shown as point A in FIG. 3. Changing the
frequency by 25 MHz to 10.025 GHz causes the reflection coefficient to
move clockwise 90 degrees from point A to point B. Different changes in
the source reflection coefficient may be achieved through corresponding
changes in the measurement frequency.
In order to provide the desired broad constellation of reflection
coefficients, other source terminations are used as well with this
frequency shifting technique. For example, the delay line may be
terminated with an open circuit, a short circuit to ground, or other
arbitrary terminations.
Also, in accordance with the present invention, a plurality of noise power
meters is connected to the DUT via a power divider. Each power meter is
configured to measure noise power within closely spaced frequency ranges.
The DUT's noise power is accordingly measured within each frequency range
simultaneously, saving much measurement time.
It is therefore a principle object of the present invention to provide for
measurement of a DUT's noise power for different source admittances within
different frequency ranges simultaneously.
It is another principle object of the present invention to provide for
simultaneous measurement of a DUT's noise figure for matched source
admittance terminations within different frequency ranges.
It is yet another principle object of the present invention to provide a
one-port tuner which produces various, predetermined source admittances
and is usable with frequency shifting techniques in a broader
constellation than has previously been possible.
The foregoing and other objectives, features and advantages of the present
invention will be more readily understood upon consideration of the
following detailed description of the invention taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph of noise factor F on a rectangular source admittance
plane.
FIG. 2 is a Smith chart graph of source reflection coefficients which
product constant noise factors F.
FIG. 3 is a graph of source admittance movement caused by frequency shift
on a Smith chart.
FIG. 4 is a block diagram of an exemplary system configuration for
measuring the noise parameters of a two-port network according to the
present invention.
FIG. 5 is a diagram of an input box of the noise parameter measuring system
of FIG. 4.
FIG. 6 is a diagram of an output box of the noise parameter measuring
system of FIG. 4.
FIG. 7 is a block diagram of a down-conversion stage of the noise parameter
measuring system of FIG. 4.
FIG. 8 is a block diagram of a noise figure meter of the noise parameter
measuring system of FIG. 4.
FIG. 9 is a diagram of an exemplary one-port tuner according to the present
invention.
FIG. 10 is a Smith chart showing typical source admittances available from
the one-port tuner of FIG. 9.
FIG. 11 is a Smith chart showing typical source admittances available from
a portion of the one-port tuner of FIG. 9.
FIG. 12 is a diagram of a second exemplary embodiment of a one-port tuner
according to the present invention.
FIG. 13 is a Smith chart showing typical source admittances available from
the one-port tuner of FIG. 12.
FIG. 14 is a Smith chart showing typical source admittances available from
a portion of the one-port tuner of FIG. 12.
FIG. 15 is a schematic diagram of a third exemplary embodiment of a
one-port tuner according to the present invention.
FIG. 16 is a Smith chart showing typical source admittances available from
the one-port tuner of FIG. 15.
FIG. 17 is a schematic diagram of a fourth exemplary embodiment of a
one-port tuner according to the present invention.
FIG. 18 is an admittance chart showing typical source admittances available
from the one-port tuner of FIG. 17.
FIG. 19 is a block diagram of a fifth exemplary embodiment of a one-port
tuner according to the present invention.
FIG. 20 is a Smith chart showing typical source admittances available from
the one-port tuner of FIG. 19.
FIG. 21 is a schematic diagram of a sixth exemplary embodiment of a
one-port tuner according to the present invention.
FIG. 22 is an admittance chart showing typical source admittances available
from the one-port tuner of FIG. 21.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, and with specific reference to FIG. 4, a block
diagram of an exemplary noise parameter testing system 10 according to the
present invention is shown. The system 10 comprises an automatic network
analyzer 12, an input box 14, an output box 18, a power divider 20 having
a plurality of outputs 20a, a plurality of noise meters 22 connected to
respective outputs 20a of the power divider 20, and a calibrated noise
source 24. The system may also comprise a down-conversion stage 19 between
the output box 18 and the power divider 20. A device under test (DUT) 16
is connected between the input box 14 and the output box 18 for testing.
Referring now to FIG. 5, the input box 14 comprises a one-port tuner 28, a
three-position switch 30, and an input bias circuit 32. The three-position
switch 30 is connected to the input port of the DUT 16 via terminal 31 and
may be selectively connected to the network analyzer 12 (FIG. 4) via
terminal 29, the one-port tuner 28, or the noise source 24 (FIG. 4) via
terminal 33. The input bias circuit 32 comprises a capacitor 32a and an
inductor 32b, and is connected via terminal 32c to a variable DC bias
source which may be adjusted to bias the DUT 16 for proper operation.
As shown in FIG. 6, the output box 18 comprises an output bias circuit 34,
a two-position switch 36, and a low noise amplifier 38. The two-position
switch 36 is connected so the output port of the DUT 16 (connected to
terminal 35) may be selectively connected to either the network analyzer
12 via terminal 37 or the low-noise amplifier 38. The low-noise amplifier
is connected to the power-divider 20 (FIG. 4) via terminal 39. The output
bias circuit 34 comprises an inductor 34a and a capacitor 34b, and is
connected via terminal 34c to a variable DC bias source which may be
adjusted to bias the DUT 16 for proper operation.
FIG. 7 shows the down-conversion stage 19 which may be included in the
noise parameter testing system. The down-conversion stage 19 uses a local
oscillator 84 tuned to a predetermined frequency and a mixer 82 to convert
the frequency of the signal output from the output box (connected to
terminal 80) to a lower frequency signal. A filter 86 connected to the
output of the mixer 82 eliminates unwanted signal components from the
mixer output. The output terminal 88 of the conversion stage 19 may be
connected to another down-conversion stage, further altering the signal's
frequency, or to the power divider 20 (FIG. 4).
Referring now to FIG. 8, each noise meter 22 may comprise a mixer 40, a
local oscillator 42, a filter 43 and comprises a noise power detector 44.
The mixer 40 and the local oscillator 42 may be used to transform the
output signal from the power divider, received via terminal 46, from
microwave frequencies to within a frequency range used by the noise power
detector 44, either supplementing or replacing the function of
down-conversion stage 19. A single local oscillator 84 may serve as an
input for mixers 82 in different noise meters 19. The term "noise meter"
is used herein to include both noise figure meters and noise power meters.
Each noise meter 22 is configured to measure noise power within different
frequency ranges. The frequency ranges are closely spaced around a
selected central frequency. As the noise performance of the DUT varies
only slightly with respect to frequency, the simultaneous measurements may
be used to calculate the DUT's noise parameters at the central frequency.
In this manner, the noise meters 22 may measure concurrently the DUT's
noise power for different source admittances. Also, in this manner, the
noise meters 22 may measure concurrently the DUT's noise figure at many
different frequencies when the DUT has a matched source impedance
termination. It will be appreciated by those skilled in the art that more
than two noise meters 22 may be used, each tuned to a different frequency,
by using a power divider 20 (FIG. 4) which has more than two outputs 20a.
The one-port tuner 28 of the input box 14 may have several configurations.
One such configuration 28a is shown in FIG. 9. A0/45-degree phase shifter
50 is connected at one side via terminal 51 to the three-position switch
30 of the input box 14 (FIG. 5), and is connected at the other side to a
power divider 52. The phase shifter 50 can selectively pass a signal
straight through without change or shift its phase by 45 degrees. The
power divider 52 has two outputs, each of which is connected to a PIN
diode 54. The PIN diodes 54 are connected to data control lines D0, D1
which control the diodes modes of operation. When the data lines are held
low the diodes conduct, having the same characteristics as a low
resistance resistor. When the data lines are held high, the diodes are
reverse biased and have the same characteristics as a low capacitance
capacitor. Changing the biases of the diodes, the reflection coefficients
seen by the outputs of the power divider change. Leake U.S. Pat. No.
4,502,028 is hereby incorporated by reference to the extent that it is
relevant in describing the operation of this tuner. One skilled in the art
will recognize that mechanical switches, as well as the electronic ones
shown, could be used to present various reflection coefficients to the
output of the power divider 52.
The reflection coefficients of this tuner seen by the DUT 16 for the four
possible states of the data lines D0 and D1 and two phase shifter states
are shown in FIG. 10. When the phase shifter passes signals straight
through, the reflection coefficients are on the central horizontal line.
When the phase shifter 50 shifts phases by 45 degrees, signals are shifted
twice (both before and after being reflected), resulting in a 90-degree
shift, also shifting the reflection coefficient 90 degrees to a vertical
line through the center of the Smith chart. The measurement frequency also
may be varied to achieve reflection coefficients not possible otherwise.
For example, the frequency may be changed to rotate the measurement points
by 45 degrees, resulting in measurement points 58.
The one-port tuner 28a shown in FIG. 9 may also be used without the
0/45-degree phase shifter 50, including only the portion 28b enclosed
within the dashed line. In this case, the power divider 52 is connected
directly to the three-state switch 30 of the input box 14 (FIG. 5). The
constellation of reflection coefficients possible from the one-port tuner
28b of FIG. 9 is shown in FIG. 11. Without frequency shift, the possible
points are on the central horizontal line of the Smith chart and
correspond to the measurement points of FIG. 10 without a phase or
frequency shift. With a frequency shift, the reflection coefficient
measurement points may be rotated around the center point of the Smith
chart. For example, the measurement frequency may be increased to cause a
90-degree rotation yielding measurement points 60. Other rotations of the
measurement points may be achieved through different changes in
measurement frequency.
Another one-port tuner 28c which may be used for the input box 14 is shown
in FIG. 12. A 0/45-degree phase shifter 90 is connected at one side to the
three-state switch 30 (FIG. 5) via terminal 91. The phase shifter's other
side is connected to a multi-position switch 92, through which the phase
shifter may be connected to different admittances, for example, an open
circuit 94, 150 ohm resistor to ground 96, 15 ohm resistor to ground 98,
and a short-circuit to ground 100. The phase shifter 90 can selectively
pass a signal straight through without change or shift its phase by 45
degrees.
The constellation of reflection coefficients possible from the one-port
tuner 28c of FIG. 12 is shown in FIG. 13. When the phase shifter 90 passes
signals straight through, the tuner's possible reflection coefficients are
on the Smith chart's central horizontal line. The open circuit maps to
point 102, while the 150 ohm resistor, 15 ohm resistor, and closed circuit
map to points 104, 106, and 108, respectively. When the phase shifter 90
shifts phases by 45 degrees, signals are shifted twice (both before and
after being reflected), resulting in a total of 90 degrees shift, also
shifting the reflection coefficient 90 degrees. Thus, the points for the
open circuit, 150 ohm resistor, 15 ohm resistor, and closed circuit move
90 degrees to points 110, 112, 114 and 116, respectively. This tuner may
be used with or without multiple measurement frequencies. If used with
multiple measurement frequencies, the frequencies may be selected to
rotate the reflection coefficient to points not achievable by the selected
phase shifter. For example, a frequency shift may be used to rotate the
points 45 degrees, yielding the measurement points 117. The noise
parameter testing system of the present invention enables
frequency-shifted measurements to be taken simultaneously with other
measurements. One skilled in the art will appreciate the phase shifters 50
and 90 used in tuners 28a and 28c, respectively, need not shift phases by
45 degrees; other amounts of phase shift also would be advantageous.
Furthermore, the phase shift may be either constant or increasing with
frequency.
The one-port tuner 28c shown in FIG. 12 also may be used without the phase
shifter 90, including only the portion 28d enclosed within the dashed
line. In this case, the multi-state switch 92 is connected directly to the
three-state switch 30 (FIG. 5) via terminal 91. The constellation of
reflection coefficients possible from one-port tuner 28d of FIG. 12 is
shown in FIG. 14. The points 118, 120, 122, and 124 correspond to open
circuit, 150 ohm resistor, 15 ohm resistor, and closed circuit,
respectively, exactly the same as shown in FIG. 13 for when the phase
shifter is set to pass signals through without a phase shift. By varying
the frequency at which the noise power is measured, the reflection
coefficients rotate around the center point of the Smith chart, a
90-degree rotation being shown by points 126, 128, 130, and 132. The DUT's
noise power may be measured simultaneously for these different source
admittances using a power divider 20 and multiple noise meters 22 as shown
in FIG. 4.
Another one-port tuner 28e for use in the input box 14 (FIG. 4) is shown in
FIG. 15. A conventional two-bit attenuator 140, having a one-decibel stage
140a and a two-decibel stage 140b, is connected to the three-position
switch 30 of the input box 14 (FIG. 5) via terminal 141. The other end of
the attenuator 140 is connected to a switch 142 which allows selective
connection to either a short-circuit to ground 144 or an open circuit 146.
With the one-decibel stage 140a unselected and the two-decibel stage 140b
selected (as shown in FIG. 15), there is a 4 dB attenuation of a reflected
signal. This maps onto the Smith chart as points 150 or 152, shown in FIG.
16, the former when switch 146 is set to the short circuit to ground, the
latter when switch 146 is set to the open circuit state. Attenuation of
two, four, or six decibels is possible with different selections of the
attenuator 140. Again, the points may be rotated around the center point
on the Smith chart by varying the frequency at which the noise power is
measured, as shown by the arrows in FIG. 16. One skilled in the art will
appreciate other terminations may be used to supplement or replace the
open and short circuit termination selectable by switch 146. One skilled
in the art will also realize that a 0/45-degree phase shifter, having the
same characteristics as described for phase shifters 50 (FIG. 9) and 90
(FIG. 12), may be interposed between the attenuator 140 and the terminal
141, with the result that the reflection coefficients shown on FIG. 16
rotate clockwise 90 degrees when the phase shifter 148 is selected to
shift phases.
Another one-port tuner 28f for use with the noise parameter testing system
of the present invention is shown in FIG. 17. Terminal 191 is connected to
the DUT 16 via the three-position switch 30 (FIG. 5). In this tuner, two
multi-position switches 190 and 192 are connected in parallel to the
three-position switch 30 (FIG. 5) of the input box. The two switches 190
and 192 allows various predetermined resistances, e.g. open circuit, 150
ohms, 50 ohms, 15 ohms, and a short circuit, to be selected in parallel
with various predetermined reactances, e.g. .+-.j50 ohms at the
measurement frequencies. The constellation available from the one-port
tuner 28f of FIG. 17 is shown in the admittance diagram in FIG. 18. When
switch 192 selects an open-circuit state, the admittance of the tuner 28f
is caused entirely by the position of switch 190. Points 194, 196, 198,
200, and 202 correspond to the tuner's admittance when switch 192 selects
the open-circuit, 150-ohm resistor, 50-ohm resistor, 15-ohm resistor, and
short-circuit. Switch 192 allows various complex admittances to be added
in parallel, moving the measurement points along the constant conductance
lines of the admittance chart. For example, when switch 192 selects
inductor L1, inductor L2, capacitor C1, and capacitor C2, where inductor
L1 has more inductance than inductor L2 and capacitor C1 has less
capacitance than capacitor C2, the admittances are shown by points 204,
206, 208, and 210, respectively. Tuner 28f may be used with the
measurement frequency shift technique which would allow multiple
measurements to be taken simultaneously. One skilled in the art will
appreciate the switches could be mechanical or electronic, such as diodes,
and also that the possible states in FIG. 18 can also be achieved by using
one multi-position switch.
Another one-port tuner 28g is shown in FIG. 19 and its corresponding
constellation in FIG. 20. The tuner 28g comprises a circulator 240, a
variable gain amplifier 245, a variable phase shifter 246, and a variable
bandpass filter 248. The circulator 240 is connected so all signals
received from the DUT 16 via terminal 250 are passed to the amplifier 245,
and all signals received from the variable bandpass filter 248 are passed
to the DUT. For realization of the tuner 28g using actual circuitry, a
fixed gain amplifier 242 and a variable attenuator 244 may replace the
variable gain amplifier 245. Assume for purposes of explanation that the
bandpass filter 248 passes all signals without attenuation or phase shift.
Then any arbitrary reflection coefficient (as seen by the DUT) could be
achieved by varying the gain of the variable amplifier and the shift
caused by the variable phase shifter 246. If the gain of the amplifier 245
is zero, no signal is returned to the DUT, resulting in a reflection
coefficient of zero, or a matched impedance, as shown by point 260 in FIG.
20. If the amplifier 245 has unity gain, the resulting reflection
coefficient will be on the perimeter of the Smith chart, its phase
determined by the amount of shift caused by phase shifter 246.
Furthermore, if the amplifier 245 has gain greater than unity, the
reflection coefficient will be outside the unity circle of the Smith
chart; this situation is useful to counteract any attenuation between the
tuner 28g and the DUT. Thus, for an arbitrary point 262 (FIG. 20), the
magnitude 264 of the reflection coefficient is determined by the gain of
the amplifier 245, and the phase 266 is determined by the shift caused by
phase shifter 246.
The bandpass filter 248 attenuates all signals outside its passband which
preferably is centered on the measurement frequency of the noise meter 22
(FIG. 4). For example, assume the amplifier 245 and phase shifter 246 are
set for reflection coefficient shown by point 268. The variable bandpass
filter 248 blocks all signals outside its passband, resulting in a
reflection coefficient of zero, as shown by point 260. The filter 248
passes signals within its passband and returns them to the DUT. Line 270
represents the path of the reflection coefficient with increasing
frequency, point 268 representing the reflection coefficient at the center
of the passband. The bandpass filter 248 allows the tuner to have an
arbitrary desired reflection coefficient at the measurement frequency and
a zero reflection coefficient elsewhere. This allows instability regions
of the DUT to be avoided.
Another one-port tuner 28h is shown in FIG. 21 and is somewhat similar to
the tuner 28f of FIG. 17. This tuner 28h comprises a multi-position switch
280 which allows selection of various admittances, e.g., open circuit 282,
15 ohm resistor 284, 50 ohm resistor 286, and 150 ohm resistor 288. The
tuner also comprises a series of delay circuits 290 having switches to
ground 292 therebetween. The delay circuits 290 and switch 292 cooperate
to provide a variable length transmission line 296. By closing switch
292a, the transmission line 296 effectively a shorted stub of length
.tau..sub.1 +.tau..sub.2 +.tau..sub.3. Different effective lengths of
shorted stubs are available by closing a different switch 292. As the
measurement frequency increases, a given variation in length of
transmission line 296 has an increasing phase shift effect. The delay
circuits 290 may be arranged in increasing delay, to counter this effect.
The resistors 284, 286, and 288 may be alternately selected in parallel
with the transmission line 296 to provide a broader constellation of
measurement points shown in FIG. 22. The points around the perimeter of
the Smith chart, shown as points 298a-298e, depict exemplary coefficients
achievable when switch 280 selects open circuit 282. The different
rotations around the chart are caused by different effective lengths of
the transmission line 296. The points within the interior of the Smith
chart show exemplary reflection coefficients corresponding to the
effective lengths of transmission line 296 in parallel with different
conductances selected by switch 280. Points 299a-299e represent reflection
coefficients achievable with the 150 ohm resistor 288 selected. Likewise,
points 300a-300e and 301a-301e represent exemplary reflection coefficients
achievable with the 50 ohm resistor 286 and the 15 ohm resistor 284
selected, respectively. A change in the measurement frequency rotates the
shown points around the center of the Smith chart.
The terms and expressions which have been employed in the foregoing
specification are used therein as terms of description and not of
limitation, and there is no intention, in the use of such terms and
expressions, of excluding equivalents of the features shown and described
or portions thereof, it being recognized the scope of the invention is
defined and limited only by the claims which follow.
* * * * *
|
|
 |
|
 |
Description |
|
