Changes

Most popular two-conductor transmission line types like microstrip, stripline, coplanar waveguide (CPW), <i>etc</i>., feature a single dominant TEM or TEM-like propagating mode. Therefore, they can be reasonably modeled using quasi-static methods. [[EM.Ferma]] takes the cross section of an infinitely long 2D transmission line structure and encloses it by a PEC domain box. Shielded transmission lines are naturally well-represented using this approach. To model open-boundary transmission lines like a microstrip line, you must place the domain boundary walls far enough from the signal line.

A microstrip line consists of a metallic strip printed on top of a dielectric substrate with a conductor backing on its other side. Click on the <b>Microstrip Wizard</b> button [[Image:MicrostripWizardIconx.png]] button of the Wizard Toolbar or select the menu item '''Tools &rarr; Transmission Line Wizards &rarr; Microstrip Line'''.

Open the property dialogs of the three material groups and examine their parameters. The fixed voltage of the "STRIP" PEC group is 1V, while the fixed voltage of the "GROUND" PEC group is 0V. The geometry created by the wizard is fully parameterized. Open the variables dialog and review the list of the variables used for the definition of the microstrip line. Change the value of "strip_wid" to 4.62893mm. You will notice that the "sub_size" will change to 46.2893mm.

Also, note that the wizard defined a vertical X-directed field sensor observable called "FS1", which is centered at (0, 0, 0). Next, right-click on the '''2D Solution Planes''' under the "Computational Domain" section of the navigation tree and select '''2D Domain Settings...''' from the contextual menu. This opens up [[EM.Ferma]]'s "2D Static Domain Settings" dialog. At the top of the dialog, you will a checked box labeled "Treat Structure as Longitudinally Infinite across Each Solution Plane Defined Below". Then in the solution planes table, you see one entry called "SP1", of quasi-static type, which is associated withe field sensor "FS1". Select and highlight "SP1" in the table and click the {{key|Edit}} button of the dialog.  {{Note| Before you can define a 2D solution plane, you must first define a field sensor observable.}} <table><tr><td> [[Image:Ferma L7 Fig6.png|thumb|left|640px|EM.Ferma's 2D static domain settings dialog.]] </td></tr></table> A new dialog titled "Add/Edit 2D Solution Plane" opens up. It is here in this dialog where you associate a new solution plane with an existing field sensor plane. By checking the box labeled "Perform 2D Quasi-Static Simulation", you instruct [[EM.Ferma]] to calculate the characteristics impedance and effective permittivity of your 2D transmission line structure as described in the beginning of this tutorial lesson.  <table><tr><td> [[Image:Ferma L7 Fig7.png|thumb|left|480px|EM.Ferma's "Add/Edit 2D Solution Plane" dialog.]] </td></tr></table>

You saw earlier that the variable "strip_widsub_size" was defined as a function of the variable "z0strip_wid". This means that "strip_widsub_size" is a dependent variable, while "z0strip_wid" is an independent variable. You can easily change the definition of any variable and turn it into an independent or dependent variable. Open the variable dialog and change the values of two variables "h" and "strip_wid" according to the table below:

| microstrip_design(z0,er)*h4.62893

Run the sweep simulation. It may take a while as a total of eleven individual 2D electrostatic simulations must be completed. At the end of the parametric sweep, open the data manager and plot the data files "SP1_Z0_Sweep.DAT" and "SP1_EpsEff_Sweep.DAT" in EM.Grid. You should see graphs like the figures below. They shows that the forward-scatter RCS is maximized at &theta; = 135&deg; as you would have expected.

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