microwave software®
MStrip+® User Manual
Transmission Line Analysis and Synthesis Utility
MICROSTRIP MODULE
A microstrip transmission line is formed by etching
a line on the top surface of a single sheet of dielectric material; the
backside plating forms a ground plane. Think of it as a piece of
coaxial cable, slit down the middle, and then peeled
apart.
Introduction
Propagation of a signal down the line is in a "quasi-TEM" mode. This means that part of the signal is in air, and part is in the dielectric. Because of this quasi-TEM mode, you must use an effective relative dielectric constant, ER', to compute line lengths. The value of the effective relative dielectric constant will be between "1," (the dielectric constant of air), and ER, the relative dielectric constant of the board material.
Microstrip is a dispersive medium. This means that the characteristic impedance and the effective relative dielectric constant both vary with frequency. These parameters also vary with cover height. MStrip+ will let you examine all these effects.
The characteristic impedance of a single-line microstrip, Z0, and the effective relative dielectric constant, ER', are a function of the following physical and electrical parameters:
- Line width
- Dielectric thickness
- Dielectric constant
- Metallization thickness
- Frequency
- Cover height
The parameter H2/H
is the cover height ratio, i.e., the ratio of air space above the
dielectric to the thickness of the dielectric. In "open
microstrip", the cover is considered to be either not
there or at infinite
height. In general, an open microstrip condition will exist
if the space above the board is greater than approximately
10 dielectric thicknesses. MS will assume
open microstrip, in its calculations, if you set the parameter H2/H=0.
By the same token, MS will do a "DC analysis," i.e., calculate at "zero frequency," if you set F=0.
To either synthesize or analyze microstrip lines under real world conditions, enter real values for H2/H and F when asked. You can examine the effects of frequency and varying cover height by using the "Tabular Data" mode.
Synthesis Mode
Enter Z0,T,H,Er,H2/H,F [<Enter>=Quit] ? _
Enter each of the six values requested. You must enter all six even if one or more are set equal "0." The units are ohms, inches, and MHz. For "open microstrip" and/or a "DC analysis," enter "0" for H2/H, F, or both.
Let's try a microstrip line synthesis of an open 50 ohm line on 30 mil Teflon-Glass (ER=2.55) with 1 oz. copper metallization.
Note: 1 oz. = 0.0014 in. = 1.4 mils.
Enter the data as follows and then press <Enter>:
50,.0014,.03,2.55,0,0
Note: At this point, you'll be asked "Print Logfile (Y/N) [<Enter>=No] ? _" Please press <Enter>.
If you choose the option to 'Print Logfile,' the data will be directed to 'Logfile.txt' within the \mwdata3 sub-directory, and to the screen. Right-click on 'Logfile.txt' to print it, and then DELETE the file; it will re-create when next needed.
MStrip+ will now display the input data on-screen, if you pressed <Enter>, and then enter a two-tiered iterative loop. Your screen should look as follows:
Follow the on-screen instructions to "- Press any Key -"
and return to the Microstrip Menu.
Let's try it once again, but this time, let's see what happens at 12 GHz with the cover placed 0.15 in. (H2/H=5) above the board. Choose "Synthesize" from the menu and enter the following data:
50,.0014,.03,2.55,5,12000
Now press <Enter> and you'll see the following:
Note that the 50 ohm line width increased by about 5%, while the change in the effective relative dielectric constant, ER', decreased by about 1.1%. If you were designing a broadband circuit, say covering 2-18 GHz, at what frequency would you set the width of the line to be 50 ohms? Think about it.
Follow the on-screen instructions to " - Press any Key - " to return to the Microstrip Menu.
Analysis Mode
Enter W,T,H,Er,H2/H,F [<Enter>=Quit] ? _
The format is the same as before; the only difference is that now we enter "W" instead of "Z0." You still must enter all six values even if one or more are "0." Again, the units are ohms, inches, and MHz. For "open microstrip," and/or a "DC analysis," enter "0" for H2/H. F, or both.
Try this out using the output data from the last line synthesis example. Enter the following:
.0875,.0014,.03,2.55,5,12000
Now press <Enter> and you'll see the following:
You'll note that there is a small difference in the two output values. It is caused by round-off error between the 4 decimal place data that you entered, and the number required to make the line exactly 50 ohms.
Let's try this mode using the same 50 ohm line as before. We'll assume that we dimensioned the line to be 50 ohms at 2 GHz, and then look at what happens, because of dispersion, over the 2-18 GHz range.
Choose "(2) Z0 vs F" from the "Tabular Data" menu. You'll see the following:
Z0 vs F Mode
Enter F Start, Stop, Step [<Enter>=Quit] ? _
Type in the following and press <Enter>.
2000,18000,2000
Now enter the line data as requested by the prompt and press <Enter> once again.
50,.0014,.03,2.55,0
Choose on-screen output, MStrip+ will now calculate the effects of dispersion over the 2-18 GHz range, in steps of 2 GHz, for a 50 ohm open (infinite cover height), microstrip whose width was calculated at the 2 GHz start frequency.
Follow the on-screen instruction to " - Press any Key - " to return to the "Tabular Data" menu.
By the same token, MS will do a "DC analysis," i.e., calculate at "zero frequency," if you set F=0.
To either synthesize or analyze microstrip lines under real world conditions, enter real values for H2/H and F when asked. You can examine the effects of frequency and varying cover height by using the "Tabular Data" mode.
The Microstrip Menu
When use choose "(1) MS" from the Main Menu,
either by pressing "1" and then <Enter>,
or by using the "F1" function key, you'll enter the Microstrip
Module. The screen display will look as follows:
| Microstrip Menu
|
| (1) Synthesize
|
| (2) Analyze
|
| (3) Tabular Data
|
| (4) Main Menu
|
| Choose (1-4) ? _
|
Line Synthesis Mode
When use choose "(1) Synthesis" from the Microstrip
Menu, in the same manner as before, the screen display will
look as follows:
Synthesis Mode
Enter Z0,T,H,Er,H2/H,F [<Enter>=Quit] ? _
Enter each of the six values requested. You must enter all six even if one or more are set equal "0." The units are ohms, inches, and MHz. For "open microstrip" and/or a "DC analysis," enter "0" for H2/H, F, or both.
Let's try a microstrip line synthesis of an open 50 ohm line on 30 mil Teflon-Glass (ER=2.55) with 1 oz. copper metallization.
Note: 1 oz. = 0.0014 in. = 1.4 mils.
Enter the data as follows and then press <Enter>:
50,.0014,.03,2.55,0,0
Note: At this point, you'll be asked "Print Logfile (Y/N) [<Enter>=No] ? _" Please press <Enter>.
If you choose the option to 'Print Logfile,' the data will be directed to 'Logfile.txt' within the \mwdata3 sub-directory, and to the screen. Right-click on 'Logfile.txt' to print it, and then DELETE the file; it will re-create when next needed.
MStrip+ will now display the input data on-screen, if you pressed <Enter>, and then enter a two-tiered iterative loop. Your screen should look as follows:
| MStrip+ MS Synthesis
|
| Input Data
|
| Z0
= 50 ohms
|
| T
= .0014 in.
|
| H
= .03 in.
|
| ER
= 2.55
|
| H2/H =
Infinite
|
| F
= DC Analysis
|
| Iterating
|
| Z0 = 49.95230102539062
|
| Z0 = 50.00246810913086
|
| Z0 = 49.99988174438477
|
| Z0 = 49.99999237060547
|
| Output Data
|
| W =
0.0831 in.
|
| ER' = 2.1107
|
| - Press any Key -
|
Let's try it once again, but this time, let's see what happens at 12 GHz with the cover placed 0.15 in. (H2/H=5) above the board. Choose "Synthesize" from the menu and enter the following data:
50,.0014,.03,2.55,5,12000
Now press <Enter> and you'll see the following:
| MStrip+ MS Synthesis |
| Input Data |
| Z0 = 50 ohms |
| T = .0014 in. |
| H = .03 in. |
| ER = 2.55 |
| H2/H = 5 |
| F
= 12000 MHz
|
| Iterating |
| Z0 = 51.57294464111328
|
| Z0 = 50.0111198425293
|
| Z0 = 49.99974060058594
|
| Z0 = 49.99999618530273 |
| Output Data |
| W = 0.0875 in. |
| ER' = 2.1565 |
| - Press any Key - |
Note that the 50 ohm line width increased by about 5%, while the change in the effective relative dielectric constant, ER', decreased by about 1.1%. If you were designing a broadband circuit, say covering 2-18 GHz, at what frequency would you set the width of the line to be 50 ohms? Think about it.
Follow the on-screen instructions to " - Press any Key - " to return to the Microstrip Menu.
Line Analysis Mode
When use choose "(2) Analyze" from the Microstrip
Menu, as before, the screen display will look as follows:
Analysis Mode
Enter W,T,H,Er,H2/H,F [<Enter>=Quit] ? _
The format is the same as before; the only difference is that now we enter "W" instead of "Z0." You still must enter all six values even if one or more are "0." Again, the units are ohms, inches, and MHz. For "open microstrip," and/or a "DC analysis," enter "0" for H2/H. F, or both.
Try this out using the output data from the last line synthesis example. Enter the following:
.0875,.0014,.03,2.55,5,12000
Now press <Enter> and you'll see the following:
| MStrip+ MS Analysis
|
| Input Data |
| W
= .0875 in.
|
| T = .0014 in. |
| H = .03 in. |
| ER = 2.55 |
| H2/H = 5 |
| F = 12000 MHz |
| Output Data |
| Z0
= 49.9835 ohms
|
| ER' = 2.1666 |
| - Press any Key - |
You'll note that there is a small difference in the two output values. It is caused by round-off error between the 4 decimal place data that you entered, and the number required to make the line exactly 50 ohms.
Tabular Data Mode
When use choose "(3) Tabular Data" from the Microstrip
Menu, the screen display will look as follows:
| Tabular Data
|
| (1) Z0 vs W/H
|
| (2) Z0 vs F |
| (3) Z0 vs H2/H |
| (4) W/H vs Z0
|
| (5) MS Menu
|
| Choose (1-5) ? _ |
Let's try this mode using the same 50 ohm line as before. We'll assume that we dimensioned the line to be 50 ohms at 2 GHz, and then look at what happens, because of dispersion, over the 2-18 GHz range.
Choose "(2) Z0 vs F" from the "Tabular Data" menu. You'll see the following:
Z0 vs F Mode
Enter F Start, Stop, Step [<Enter>=Quit] ? _
Type in the following and press <Enter>.
2000,18000,2000
Now enter the line data as requested by the prompt and press <Enter> once again.
50,.0014,.03,2.55,0
Choose on-screen output, MStrip+ will now calculate the effects of dispersion over the 2-18 GHz range, in steps of 2 GHz, for a 50 ohm open (infinite cover height), microstrip whose width was calculated at the 2 GHz start frequency.
| MStrip+ MS Z0 vs F
Analysis
|
| Input Data
|
| Z0
= 50 ohms
|
| T
= .0014 in.
|
| H = .03 in. |
| ER = 2.55 |
| H2/H = Infinite
|
| F
Z0
ER'
|
| 2000
50.0000
2.1132
|
| 4000
50.2497
2.1195
|
| 6000 50.6576 2.1295 |
| 8000 51.2124 2.1428 |
| 10000 51.8991 2.1588 |
| 12000 52.6998 2.1766 |
| 14000 53.5954 2.1957 |
| 16000 54.5658 2.2154 |
| 18000 55.5914 2.2353 |
| - Press any Key - |
Follow the on-screen instruction to " - Press any Key - " to return to the "Tabular Data" menu.