MStrip+ User Manual - Stripline Coupled Line Module

microwave software®

MStrip+® User Manual
Transmission Line Analysis and Synthesis Utility

STRIPLINE COUPLED LINE MODULE

Introduction

Coupled strip transmission lines are formed by etching two lines, separated by a small gap, on the surface of a bottom dielectric sheet. This sheet is then sandwiched with a top board, whose metallization has been removed on one side. The backside plating of both form a ground plane. Or, if there is no metallization, the ground plane is provided by the housing or metal backing plates.

Like stripline, propagation of a signal down these lines is in a pure, and non-dispersive TEM mode. The characteristic impedance of the coupled-line pair is described in terms of their even and odd mode impedance, Zoe and Zoo. The length of a line is calculated simply by using the dielectric constant of the dielectric material.

The even and odd mode impedances, Zoe and Zoo, are a function of the following physical and electrical parameters.

Line width
Gap width
Ground plane spacing
Dielectric constant
Metallization thickness

A sketch of a typical coupled stripline is shown below. The terms used to describe it are standard in the industry.

The Stripline Coupled Line Menu

When use choose "(4) SLC" from the Main Menu, either by pressing "4" and then <Enter>, or by using the "F4" function key, you'll enter the Microstrip Coupled-Line Module. The screen display will look as follows:

Coupled Stripline Menu

(1) Synthesize

(2) Analyze

(3) Tabular Data

(4) Main Menu

Choose (1-4) ? _

Coupled-Line Synthesis Mode

When use choose "(1) Synthesize" from the Coupled Stripline Menu, in the same manner as before, the screen display will look as follows:

                Synthesis Mode

                Enter Zoe,Zoo,B,Er [<Enter>=Quit] ? _

Enter each of the four values requested. The units are ohms and inches.

Let's work thru a simple line synthesis example. It might be interesting if we do a 10 dB directional coupler at 10 GHz, the same as we did earlier in the MSC Module.

As before, standard coupler design equations give the even and odd mode impedances as 69.5 and 36 ohms, respectively. A practical material to use here would be 60 mil Teflon-Glass (Er=2.55). This would give a 0.120 in. ground plane spacing.

Enter each of the four data values requested and then press <Enter>: The units are ohms and inches.

                69.5,36,.12,2.55

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 display the input data on-screen, IF you pressed <Enter>, as follows:

MStrip+ SLC Synthesis

Input Data

Zoe = 69.5 ohms

Zoo = 36 ohms

B = .12 in.

ER = 2.55

Output Data

W = 0.0724 in.

S = 0.0063 in.

- Press any Key -

Follow the on-screen instructions to "- Press any Key -" and return to the Coupled Stripline Menu.

Coupled Line Analysis Mode

When use choose "(2) Analyze" from the Coupled Stripline Menu, the screen display will look as follows:

Analysis Mode

Enter W,S,B,Er [<Enter>=Quit] ? _

This option works the same as those shown earlier. Try working backwards using the results of the line synthesis just completed.

Tabular Data Mode

When use choose "(3) Tabular Data" from the Coupled Stripline Menu, the screen display will look as follows:

Tabular Data

(1) Zoe/Zoo vs W/B

(2) Zoe/Zoo vs S/B

(3) SLC Menu

Choose (1-3) ? _

Zoe/Zoo are in ohms, awhile W/B and S/B are ratios.

Note that values of the independent variables, W/B and S/B, must be >= .01

The following is a tabulation of Zoe/Zoo vs W/B on Teflon-Glass, (Er=2.55), with S/B held constant at 0.3

Choose "(1) Zoe/Zoo vs W/B" from the Tabular Data menu.

                Zoe/Zoo vs W/B Mode

                Enter W/B Start, Stop, Step [<Enter>=Quit] ? _

Type the following and press <Enter>.

                .1,1,.1

Next, enter the line data as requested by the prompt and press <Enter> once again.

                .3,2.55

You'll see the following on-screen:

MStrip+ SLC Zoe/Zoo vs W/B Analysis

Input Data

S/B = .3

ER = 2.55

W/B Zoe Zoo

0.10 143.8676 99.1891

0.20 112.2734 78.7239

0.30 93.4753 67.5444

0.40 80.4139 59.8808

0.50 70.6661 54.0630

0.60 63.0672 49.3950

0.70 56.9605 45.5215

0.80 51.9392 42.2351

0.90 47.7346 39.4021

1.00 44.1612 36.9304

- Press any Key -

Follow the on-screen instruction to " - Press any Key - " to return to the Tabular Data menu.

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