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1992-01-29
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SCAT V2.0
Scattering Parameters Program
(C) 1991,92 by J.Herron
CONTENTS
1. Introduction.....................2
2. Installation.....................2
3. How To Use Help..................2
4. Menus Explained..................3
5. Functions Available..............3
6. File Operations..................3
7. Unilateral Analysis..............5
8. Bilateral Analysis...............6
9. Noise Analysis...................9
10. Matching........................9
11. Using The Chart................10
12. Options Menu...................11
13. Example1.......................12
14. Example2.......................12
15. Example3.......................13
16. Registration...................14
17. References.....................14
James Herron
Aciran Software Systems,
29 Duncryne Place,
BishopBriggs,
Glasgow G64 2DP
Scotland.
Page - 1
Introduction.
This program computes a number of useful S-Parameter functions and makes use
of a Smith Chart to display the results. After starting the program and
observing the copyright notice the user is presented with the main screen
which is divided into three sections.
At the top is the menu selection which allows access to the various functions
performed by SCAT. At the left of the screen is the information window which
is where SCAT outputs information about the Device that is being analysed.
The area between the menu and information window is the chart where most
results and input forms appear.
Installation.
SCAT can be run from a single floppy disk drive, however use off a hard disk
is recommened as the floppy disk will fill up as you create more and more data
files. First of all make working copies of you Master disks and then put them
in a safe place, use DISKCOPY as instructed in you Dos handbook. To install on
a hard disk first create a directory by typing md SCAT <return>, cd SCAT
<return>. Place you Master disk in drive A and from the SCAT directory on your
hard drive type copy a:*:* <return>. The main files are:
SCAT2.DOC This file
SCAT2.COM Loads Graphics driver then main program.
SCAT2.EXE The main program.
SCAT2.HLP Help File for On Line context sensitive help.
SCAT2.CFG Configuration file, will be created if not present.
ORDER.FRM Registration order form, Please Use it.
EGAVGA.COM Graphics driver for EGA & VGA adapters.
EGACHART.PCT The Smith Chart. SCAT forces EGA mode as this is easier to read.
PRINTER.COM Generic Printer Driver (default is HP LaserJet II).
Registered disks have the following additional files.
EPSON.COM Printer driver for Epson compatible printers.
IBMPRO.COM Printer driver for IBM Proprinter compatible printers.
HPLASER.COM Printer driver for HP LaserJet II compatible printers.
There may be a number of example data files on the disk, but these
are not essential to the operation of the program. These have extension *.SPD.
Scat has a comprehensive on-line help facility, it can be accessed at any
time by pressing the F1 key. A help box will open on the screen at a page
relevent to where you are in the program.
How to use Help
You can move around in help by pressing the PgUp or PgDn keys
to move one page at a time, or you can use a mouse and select the
direction to move in by pointing to the scroll bar at the side of
the help window and clicking the left mouse button. Exit Help by
pressing the Esc key or use the mouse to click on the cancel button.
Page - 2
A number of option buttons appear at the bottom of the help box. You
can select a button by using the mouse or cursor keys. For example if
you select index you will see an alphabetic list of subject headings
along with page numbers. If you point to the heading and click the
left mouse button you will jump to that page. To use the keyboard press
tab to enter the window and use the cursor keys to scroll up and down
to reach your choice, then press enter and you will jump to that page.
The Menu System
How to use the menus
When Scat starts you will be presented with a menu which has a
number of choices.
File Unilateral Bilateral Noise Matching Chart Options
The sign on screen displays a copyright notice and after a few
seconds the Smith chart is loaded and displayed.
There are two ways in which you can select a menu option, depending on
whether or not you have a mouse fitted.
The Use of the KeyBoard and Mouse
Keyboard Only
If you only have a keyboard then you enter the menu by pressing the
F10 key. This will pull down the first menu option, and you use the
cursor keys to move around the different selections available.
Once you have highlighted your choice simply press return to select it.
Certain menu choices may not be available depending on the type of
device being used, and on the data present, eg S-Parameters and/or
Noise data.
Mouse Option
If you have a mouse simply point to the menu and click the left mouse
button to open it. Next point to the selection of your choice within
the menu and click the left button again.
The Menus Explained
What the menu options mean
File
This menu presents the following options.
System Reset
New Scattering Parameters
Edit Scattering Parameters
Load a File
Save a File
Quit to Dos
Each will be briefly explained. For Detailed information please
consult the printed manual.
Page - 3
System Reset
Choose this option to reset the system to its initial start-up state.
You will be warned that all data will be lost. You should select this
option if you wish to start work on a new device which has only Noise
or Scattering parameter data, but not both, otherwise you may find you
have inherited some Noise or Scattering parameters from any previous
device in memory.
New Scattering Parameters
Select this option to enter New Scattering Parameter Data. A fill-in
form will appear and you should enter the information requested. The Zo
field is already filled in with the current Zo value. You can move
through each field in turn, or jump around, perhaps to correct an
error,by using the cursor keys or mouse to select any field. Click on
the continue button when complete, or select the cancel button or press
Escape to abort.
All scattering parameter magnitudes must be greater than zero, all
angles must lie between -360 and +360 degrees. Any attempt to violate
these input conditions will result in an error message, and the form
will re-appear for correction.
You may abort input at any time up to the last entry by simply pressing Esc.
Enter all the S-parameters including a device ID and the frequency at which
measurements were made. This last information is not used in any calculations,
it is purely for reference and is shown on Graphs to help you identify which
device was used. The device ID would normally be the component type, eg BFP96.
Edit Scattering Parameters
This option is similar to the New Parameters option except the form
contains the current data values for editing purposes. You can select
any fields you want to change (except Zo), and once satisfied select
the continue button to change the data, or press the cancel button or
Escape key to abort.
Load a File
This allows you to retrieve previously saved data by selecting
the appropriate File. When this option is selected a Load Box will
pop up on the screen and you will be prompted to select the data
file to be loaded.
Use the mouse or cursor and return keys to move through the folders
to reach the file you want to use, the Tab key will give access to the
three buttons which allow you to change drive,enter a folder, or cancel
the operation. When selected the Load Box will close and the file will
be read by the computer.
Most operations cannot be performed until either the S-parameters or noise
data have been entered or loaded, and this brings us to the next menu option.
The component data file may contain either S-parameter data or noise data or
both. The operations allowed will depend on what information is available.
There is no reason why you could not enter only Noise data and perform noise
analysis if that is all you required, S-parameters data can be added later if
desired.
Page - 4
Save a File
This allows you to save newly entered data by entering a File name.
When this option is selected a Save Box will pop up on the screen
and you will be prompted for a Dos file name. If the data was loaded
previously from a file, that name will appear in the save box and
you may accept it or change it to another.
Use the mouse or cursor and return keys to move through the folders
to reach the directory you want to use, the Tab key will give access
to the three buttons which allow you to change drive,enter a folder,
or cancel the operation. When selected the Save Box will close and the
file will be written to disk by the computer.
Quit to Dos
As the name suggests this option allows you to exit the program and
return to DOS. If you have changed your data you will be asked if you
wish to save it. You also will be asked to confirm exit to Dos.
Unilateral Menu
This menu has the following options.
Gain analysis
Plot Gain Circles
Each will be described briefly, see printed manual for more details.
Gain Analysis
This options performs a Unilateral analysis on the device. This option
will display a table of Unilateral parameters including the Stability
factor K, the unilateral figure of merit U, and the min and max gains
available for the device connected to Zo source and load impedances,
and the additional gain contributions possible for conjugate matching
of the source and load. Refer to the manual for a fuller explaination.
The following equations are used:-
U = |S11 S12 S21 S22 |
|(1-|S11|^2) (1-|S22|^2)|
Gu = |S21|^2
|(1-|S11|^2)(1-|S22|^2)
Gmin = 1 Gmax = 1
(1+U)^2 (1-U)^2
Go = |S21|^2 = transducer gain for Zo input and output impedance.
Gu = Go * G1 * G2 G1max = 1 G2max = 1
1-|S11|^2 1-|S22|^2
Page - 5
[Unilateral Analysis]
U = 0.09
Gu = 6.02dB
Ga min = 5.25dB
Ga Max = 6.86dB
Go = 2.28dB
G1 max = 3.17dB
G2 max = 0.57dB
Fig 1.
Press the continue button to remove the table, or press the Print It
button to obtain a printed report.
Plot Gain Circles
Use this option to construct input and output gain circles for a
Unilateral amplifier design. The circles can be used for an inheritly
stable device which is being treated as Unilateral. A form will appear
requesting gain contributions required from the source and load. The
max values availble are shown in brackets. The constant gain circles
for source and load will be drawn on the chart. The output circle is
drawn thicker to distinquish it from the input circle on mono monitors
and when copied to the printer.
The following equations are used:-
roi = Gi Sii poi = sqrt(1-Gi*(1-|S11|^2))
1+Gi|Sii|^2 1 + Gi *|Sii|^2
center of circle radius of circle
Bilateral
This menu has the following options.
Simultaneous Conjugate Match
Bilateral Stability Circles
Plot Bilateral Gain Circles
Each will be described briefly, see printed manual for more details.
Simultaneous Conjugate Match
If the device in memory has a stability factor K greater than unity it
is inherently stabily and can be conjugately matched for maximum gain
without worry of instability due to input or output loads placed on
the device. Choose this option to get the source and load impedances
and reflection coefficients for conjugate matching, and the value of
maximum available gain. If the device is unstable it will not be
possible to select this menu option.
When the results are presented you may print a Report by clicking
on the Print button, ensure the printer is ready.
Page - 6
The following equations are used:-
K = 1+|D|^2 - |S11|^2 - |S22|^2
2|S21*S12|
where D = (S11*S22-S21*S12)
Gmax = | S21 * (K+/- sqrt(K^2 - 1)) |
| S12 |
the plus sign is used when B1 is negative and the negative sign is used when
B1 is positive, where
B1 = 1 + |S11|^2 - |S22|^2 - |D|^2
The optimum source and load impedances are calculated from
Tms = C1* * |B1 +/- sqrt(B1^2-4|C1|^2)|
| 2*|C1|^2
TmL = C2* * |B2 +/- sqrt(B2^2 -4|C2|^2)|
| 2*|C2|^2
where C1 = S11 - D * S22* and C2 = S22 - D & S11*
C1* = complex conjugate of C1, C2* = complex conjugate of C2.
B1 = 1 + |S11|^2 - |S22|^2 - |D|^2
B2 = 1 + |S22|^2 - |S11|^2 - |D|^2
Bilateral Stability Circles
If a device is unstable use this option to plot the input and output
stability circles. The output circle is drawn thicker to differentiate
it from the input circle. Refer to the manual to determine whether the
inside or outside of the stability circle is the stable region.
This option will plot Bilateral stability circles on the Smith Chart. The
output stability circle is plotted thicker than the input circle to distinguish
them on a mono screen or printer.
The following equations are used:-
rsi = | Ci* | psi = | S21 * S12 |
| |Sii| - |D|^2 | | |Sii|^2 - |D|^2 |
rs1 = location of center of stability circle on I/P plane
rs2 = location of center of stability circle on O/P plane
ps1 = location of radius of stability circle on I/P plane
ps2 = location of radius of stability circle on O/P plane
These circles indicate the boundary between stable and unstable regions, they
do not indicated which is which. The area either inside or outside the circle
will represent a stable operating condition.
Page - 7
To determine which area represents this stable operating condition, let's
make ZL = 50 ohms, or TL = 0. This represents the point at the center of the
Smith chart. Under these conditions |Ts| = |S11|.
Let's now assume that S11 is less than one, Ts is also less than one, this
means that the point TL = 0 represents a stable region. If we select another
value of TL that falls inside the stability circle we would have a potentially
unstable situation.
If on the other hand |S11| > 1 with ZL = 50, then this area would be the
stable region.
Caution: S-Parameters are typically measured at some particular frequency.
The Stability circles are draw for that frequency. We cannot be sure that the
device will be stable at other frequencies unless you check them out.
Plot Bilateral Gain Circles
Use this option to plot constant gain circles for a Bilateral amplifier
design. If the device is stable the input form requests the gain
required and shows the maximum available in brackets. For unstable
devices the maximum gain in indeterminant, however gain circles can
still be plotted, and a warning given if the value entered cannot be
achieved. See the manual for more details including worked examples.
This option is for Bilateral gain circles. The gain required is input in dB
and load gain circles are plotted on the Smith Chart. The following equations
are used:-
ro2 = | G | * C2*
| 1+D2*G |
center of circle
po2 = |sqrt((1-2K|S12*S21|*G+|S12*S21|*2*G^2))|
| 1 + D2 * G |
radius of circle
where G = Gp/Go Gp = desired gain, and Go = |S21|^2
the transducer gain
D2 = |S22|^2 - |D|^2
New Noise Data
Select this option to enter Noise data. A form will appear and you
should fill in the necessary information. Note that the noise
resistance is in ohms and NOT normalised as in some manufacturers
data sheets. Fmin is the min noise figure for the device (at the
frequency stated) and is in dB and must be greater than zero.
Edit Noise Data
Use this option to edit noise data previously entered. The data will
be verified to be consistent with practical devices, eg Fmin must be
greater than zero.
Page - 8
Plot Noise Circles
You will be asked to enter the noise figure to plot. This must be
greater than or equal to Fmin, if not an error message will be
given and the form will reappear for correction.
The data required is Rn (ohms), Fmin (dB), Optimum noise source (magnitude and
angle). Finally enter the noise figure to be plotted.
The following equations are used:-
Center of circle = CFI = To
1 + Ni
and radius = sqrt(Ni^2 + Ni*(1-|To|^2))
1 + Ni
where To = optimum Noise source reflection coefficient fo Fmin
Ni = Fi - Fmin where Fi = Noise Figure Requested
4*rn rn = Rn = Normalised equivalent
Zo noise resistance.
Be careful when using manufacuters data sheets as some give Rn (ohms) and
others rn (normalised to Zo).
Source Match for Given Load
Use this option to calculate the conjugate Source matching
impedance (reflection) for the device, when connected to a given
Load. You will be presented with a choice of entering Impedance
or Reflection coefficients. Tick the box for the type of input
you want to use. If you select impedance you will be asked for the
load impedance in terms of a real and imaginary impedance. If you
selected Reflection you will be asked for the magnitude and phase of
the reflection.
You will then be presented with the value of source impedance and
its corresponding reflection coefficient, and the values of maximum
transducer gain GT and max operating gain GP.
When the results are presented you may print a Report by clicking
on the Print button, or Plot the source impedance by clicking Plot.
This option calculates the optimum source impedance given the desired Load
impedance placed on the device output. The following equations are used:-
RmL = | Sii - RmL*D |* where RmL = Load impedance in the
| 1 - RmL*S22 | form (X + jY) ohms
Load Match for Given Source
Use this option to calculate the conjugate Load matching
impedance (reflection) for the device, when connected to a given
Source. You will be presented with a choice of entering Impedance
or Reflection coefficients. Tick the box for the type of input
you want to use. If you select impedance you will be asked for the
source impedance in terms of a real and imaginary impedance. If you
selected Reflection you will be asked for the magnitude and phase of
the reflection.
You will then be presented with the value of load impedance and
its corresponding reflection coefficient, and the values of maximum
transducer gain GT and max operating gain GP.
Page - 9
When the results are presented you may print a Report by clicking
on the Print button, or Plot the load impedance by clicking Plot.
This option calculates the Load impedance for optimum matching, given the source impedance placed on the input of the device.
The equation used is
TmL = | S22 - RmS * D | where RmS = Source impedance in the
| 1 - RmS * S11 | form (X + jY) ohms
Chart Menu
The Chart Menu has the following options:
Plot Impedance
Read Impedance
Clear Chart
Print Chart
Select Zo
Each will be described briefly, see printed manual for more details.
Plot Impedance
Use this option to plot an impedance (reflection) on the Smith Chart.
You may do this to ensure that a chosen source or load does not lie
in an unstable region. See the examples in the manual.
You will be presented with a choice of entering Impedance
or Reflection coefficients. Tick the box for the type of input
you want to use. If you select impedance you will be asked for the
impedance in terms of a real and imaginary impedance. If you
selected Reflection you will be asked for the magnitude and phase of
the reflection.
The impedance (reflection) will then be plotted on the smith chart
as a small circle.
Read Impedance
This option allows you to read impedance or reflection directly from
the chart.
You cannot use this option unless you have a mouse.
Brief instructions are given. When inside the Smith chart click on the
left mouse key to read the chart. The corresponding value of impedance
and reflecion are displayed at the bottom of the information window.
You can read the chart continuously by holding down the left button
or pressing any key (eg. space bar) while moving the mouse pointer.
If you move off the chart, or press the right mouse button, the
reading operation will terminate. You can also stop by pressing the
Escape key. Useful if you selected this option by mistake and do not
have a mouse present. Using right button copies data to input forms.
Clear Chart
Quite simply this will clear the chart by reloading it from disk.
You will be given a warning before proceeding. If you want to keep
the chart, perhaps to superimpose different sets of results, you
may cancel by pressing Escape or clicking on the cancel button.
Page - 10
Print Chart
This option will dump the chart onto a printer. You will be given
the opertunity to abort if you wish. The printer should be on-line
and have paper. Scat uses the currently selected printer driver.
Select Zo
The default value for Zo is 50 ohms. Use the option to select one
of the common values of 50,75,100,300,or 600 ohms by checking
against it's box.
Alternatively you can choose Other, and a form will appear asking
for the value of Zo you desire. Zo must be greater than Zero.
Options Menu
The Options Menu has the following options:
Select Printer
Date Format
Set Hot Keys
Each will be described briefly, see printed manual for more details.
Select Printer
Scat supports three printer drivers, these are
Epson or compatible
IBM proprinter
HP LaserJet II or compatible
You will be presented with a list of these options and you should
select one. The current driver will be highlighted. This information
is stored in a configuration file along with the Date format and the
list of user defined Hot keys. See pages #32 and #33.
Date Format
When printing Reports Scat Time Stamps them with Date and Time
information. In the UK the date format is normally DD/MM/YYYY and
in the USA it is MM/DD/YYYY. This option allows you to select the
format for you country. This information is stored in a config file
and so need only be set up once.
Set Up Hot Keys
Experienced user may prefer to bypass some or all the menus by
assigning Hot Keys to the menu items. Some have already been set,
eg control [L] to load a file. You can set your own control keys
using this option. Try to choose letters that mean something so that
you will remeber them. this info is stored in the config file.
This option gives a list of choices. You can program each menu item,
Clear a menu item, Clear alll items, or cancel out without changing
anything.
If you decide to set up a hot key, you will be asked to select the menu
item. Use the mouse to highlight the menu choice and click the left
button. A dialog box will ask you for the letter to use along with the
control key. When you exit Scat this info is saved for future sessions.
Page - 11
Examples.
Three example transistor data files are supplied. These are BFP96, HXTR3121,
and HXTR6106. The BFP96 is unconditionally stable at the frequency of interest,
the HXTR3121 is conditionally stable, and the HXTR6105 contains only Noise
data.
Example 1: HXTR6105.
This transistor is the subject of a Hewlett Packard application note number
AP17, Noise parameters and Noise Circles. Application notes are usually free
on request from HP. The example covers the transistor at 2GHz, and the
following noise data should be entered when New Noise Data is selected:
Rn = 5.04
Fmin = 2.25
|To| = 0.429
<To = 173
Zo = 50
If you do not wish to enter the parameters select Load from the File menu and
enter HXTR6105 in response to the filename. The current value of Zo is saved
and loaded as part of the data file.
Select Plot Noise Circles and enter a noise figure of 3.0
The Noise circle will be drawn on the Smith Chart, and a hard copy may be
obtained by pressing Alt-P when the chart is displayed.
A copy of the result can be seen in Graph 1, this is from an EGA display
adapter.
Example 2: HXTR3121.
This example is also based on an HP application note number AP998, A 75 ohm
470 - 806 Mhz Low noise Amplifier. The transistor parameters a 470 Mhz are:
S11 = 0.72 < -156.0
S12 = 0.04 < 31.9
S21 = 9.16 < 95.9
S22 = 0.35 < -62.0
Zo = 75
Frequency = 475 Mhz.
Either enter or load the parameters. This device is potentially unstable, so
plot the Stability Circles for this frequency. The thick circle represents the
output stability circle, the thin one the input. Select Bilateral Gain and
enter a value of 19. The output Bilateral Gain circle for 19dB will also be
drawn on the chart alongside the stability circles, see Graph 2. Any point
chosen as a load on this circle will give 19 dB gain. Select a point away from
the unstable region, (50 - j54 in this example).
Select Load/Source Matching and enter the value of Load chosen. The
corresponding input match for maximum gain is given.in terms of impedance
and Reflection.
Page - 12
Example 3: BFP96.
Enter or load the following S - Paramerters for the BFP96
S11 = 0.72 < 152.0
S12 = 0.12 < 52.0
S21 = 1.30 < 42.8
S22 = 0.35 < -87.0
Zo = 50 Frequency = 2GHz
Select Unilateral Gain, the results are shown in Fig 1. The device is stable
at this frequency. Choosing Bilateral Gain will give the K stability factor,
the Maximum gain, and the conjugate input and output match required to obtain
this gain.
Select Unilateral Circles. Enter Gain values for GS and GL equal to 3.0 and
0.5 respectively. Observe the gain circles as depicted in Graph 3. The center
of these circles is where G1 and G2 max are found. Select Unilateral circles
again and enter values of 1.0 and 0.2 for GS and GL. Observe the new circles
added to the chart. These circles along with say noise data enable the
designer to achieve the best trade off between gain and noise figure, while
keeping a watchful eye on stability.
Graph 1.
See Manual for Details.
Graph 2
See Manual for Details.
Graph 3
See Manual for Details.
Page - 13
Why Register
Scat is distributed using the Shareware principle of Try before you
buy. This is NOT a FREE program by shareware.
If you use Scat you are expected to register with the author. It is
only through your support that shareware can bring you Quality
Software at affordable prices. By supporting the Author you
encourage him to spend more time providing the extra features that
YOU want to see. If you have any comments or would like extra functions
added then feel free to write to me about them.
Registration brings the following benefits:
1. A disk containing the latest version of the program.
2. Free Technical telephone support for 6 months, and free upgrades in that
time period.
3. A printed bound manual produced on a Laser printer using Ventura DTP
containing many more examples than in this abridged version.
4. Additional printer drivers for Epson & IBM Proprinter printers.
References.
All the calculations in Scat have been tested using many worked
examples from authoritive texts on the subject of Scattering
Parameter Analysis. Some of the works referenced are:
High Frequency Amplifiers By Ralph S. Carson.
Transistor Designers Guide By Microwave Associates Ltd.
S-Parameter Design, HP Application note 154
S-Parameter Techniques for Faster, More accurate Network design,
HP Application note 95-1
A 75 Ohm 470-806 Mhz Low Noise Amplifier Using the HXTR-3121
Bipolar Transistor. HP Application note 998.
Noise Parameters and Noise Circles for the HXTR-6101,-6102,
-6104, and -6105 Low Noise transistors.
HP Application Bulletin 17.
RF Circuit Design by Chris Bowick
Page - 14
