Difference between revisions of "EM.Picasso Tutorial Lesson 10: Optimizing A Microstrip Patch Antenna Design"

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{{projectinfo|Tutorial| Optimizing A Microstrip Patch Antenna Design|Picasso L2 Fig title.png|In this project, you will use one of EM.Cube's optimziers to design a patch antenna with a recessed microstrip feed line.|
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{{projectinfo|Tutorial| Optimizing A Microstrip Patch Antenna Design|Picasso L10 Fig title.png|In this project, you will use one of EM.Cube's optimziers to design a patch antenna with a recessed microstrip feed line.|
  
 
*Wizard
 
*Wizard
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In this tutorial you will revisit the rectangular patch antenna design with a recessed feed, which you explored earlier in Tutorial Lesson 2. This time, however, you will define a design objective and will use [[EM.Picasso]]'s optimization utility to optimize the values of designated design variables to achieve your goal.   
 
In this tutorial you will revisit the rectangular patch antenna design with a recessed feed, which you explored earlier in Tutorial Lesson 2. This time, however, you will define a design objective and will use [[EM.Picasso]]'s optimization utility to optimize the values of designated design variables to achieve your goal.   
 +
 +
[[Image:Back_icon.png|30px]] '''[[EM.Picasso  | Back to EM.Picasso Manual]]'''
 +
 +
[[Image:Back_icon.png|30px]] '''[[EM.Cube#EM.Picasso_Documentation | Back to EM.Picasso Tutorial Gateway]]'''
 +
 +
[[Image:Download2x.png|30px]] '''[http://www.emagtech.com/downloads/ProjectRepo/EMPicasso_Lesson10.zip Download projects related to this tutorial lesson]'''
  
 
== Getting Started ==
 
== Getting Started ==
Line 44: Line 50:
 
== Creating the Patch Geometry with a Recessed Feed ==
 
== Creating the Patch Geometry with a Recessed Feed ==
  
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Click on the <b>Microstrip-Fed Patch Wizard</b> button of the Wizard Toolbar or select the menu item '''Tools &rarr; Antenna Wizards &rarr; Microstrip-Fed Patch Antenna'''. A dialog pops up asking you if you would like a patch design with a recessed feed. This time, answer "Yes" and let the wizard draw the geometry of the patch antenna with the recessed feed.
+
Follow a similar procedure as in Tutorial Lesson 2 and use the <b>Microstrip-Fed Patch Wizard</b> to create the parameterized geometry of a patch antenna with a recessed feed.
  
 
<table>
 
<table>
 
<tr>
 
<tr>
 
<td> [[Image:Picasso L2 Fig1.png|thumb|left|720px|The patch antenna geometry with the recessed feed in the project workspace.]] </td>
 
<td> [[Image:Picasso L2 Fig1.png|thumb|left|720px|The patch antenna geometry with the recessed feed in the project workspace.]] </td>
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</tr>
 
−
</table>
 
−
 
−
The wizard automatically created a PEC trace called "PATCH_PEC" in the navigation tree containing four rectangle strip objects:
 
−
 
−
#"ANCHOR": representing the square patch antenna 
 
−
#"Feed": representing the microstrip feed line
 
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#"Flap_1": representing the upper flap on the feed edge
 
−
#"Flap_2": representing the lower flap on the feed edge
 
−
 
−
Also, note that wizard placed the scattering wave port not that the junction between "ANCHOR" and "Feed", but an offset equal to the depth of the recessed feed. This established the phase plane for the computation of the S-parameters. If you open the property dialog of the source "WP_1", you will find that the value of its "Offset" parameter has been set equal to the variable "recess_dep". 
 
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−
<table>
 
−
<tr>
 
−
<td> [[Image:Picasso L2 Fig2.png|thumb|left|480px|The scattering wave port/source dialog.]] </td>
 
 
</tr>
 
</tr>
 
</table>
 
</table>
Line 87: Line 78:
 
| 5
 
| 5
 
|}
 
|}
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The length of the original patch antenna created by the wizard was frequency-dependent as the definition of its variable "patch_len" involved the variable "lambda0_unit", which itself depended on the project center frequency "fc". By defining numeric values for the three variables "patch_len", "recess_dep" and "recess_wid", you have now turned them into independent variables. 
 
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{{Note|Only independent variables can be designated as sweep variables for performing parametric sweeps.}}
 
  
 
<table>
 
<table>
Line 98: Line 85:
 
</table>
 
</table>
  
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The figure below shows the planar mesh of your antenna structure with a mesh density of 30 Cells/&lambda;<sub>eff</sub>:
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== Defining the Design Objective ==
−
 
+
−
<table>
+
−
<tr>
+
−
<td> [[Image:Picasso L2 Fig1A.png|thumb|left|640px|The planar mesh of the patch antenna geometry with the recessed feed.]] </td>
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−
</tr>
+
−
</table>
+
  
−
== Running a Frequency Sweep of the Resonant Patch Antenna ==
+
In this project, you will fix the side dimensions of the patch ("patch_len"), and will optimize the two feed variables: "recess_dep" and "recess_wid". But first you need to define a design objective for your project. The goal here is to achieve a good impedance match by varying the design variables. A return loss of -20dB typically represents a very good impedance match.
  
−
Open the simulation run dialog and select '''Frequency Sweep''' from the drop-down list labeled '''Simulation Mode'''.  
+
To define a design objective, click on the '''Objectives''' [[File: Objective icon.png]] button of the Simulate Toolbar or select the menu item '''Simulate &rarr; Objectives...''' [[EM.Cube]]'s Objectives dialog opens up, which is initially empty.  
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig4.png|thumb|left|480px|Setting frequency sweep as the simulation mode in EM.Picasso's run dialog.]] </td>
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<td> [[Image:Picasso L10 Fig4.png|thumb|left|480px|EM.cube's Objective dialog initially being empty.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
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Click the {{key|Settings}} button next to this drop-down list to open the Frequency Sweep Settings dialog. The default frequency sweep type is '''Uniform''', which you keep intact. Enter 2.15GHz and 2.65GHz for the start and stop frequencies, respectively, and keep the number of frequency samples at the default value of 11.  
+
Click the '''Add''' button of this dialog to open "Add Objective" dialog. At the bottom of this dialog you will see a list of [[EM.Cube]]'s available standard output parameters. The contents of this list vary depending on the observables you have already defined for your project. Since the wizard created a port definition for this project, you will see a number of standard output parameters related to the S/Z/Y parameters. A design objective is defined as a logical statement:
  
−
<table>
+
''expression_1'' ''logical operator'' ''expression_2''   
−
<tr>
+
−
<td> [[Image:Picasso L2 Fig5.png|thumb|left|480px|EM.Picasso's frequency sweep settings dialog.]] </td>
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−
</tr>
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−
</table>
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Close this dialog to return to the run dialog and click the {{key|Run}} key to start the frequency sweep. After the completion of the sweep simulation, open the data manager and plot the data files "S11_Sweep.CPX" and "Z11_Sweep_CPX" in EM.Grid. Note that you can make multiple file selections for plotting using the {{key|Ctrl}} or {{key|Shift}} keys.
+
The first and second expressions can be any mathematical expression involving the standard output parameters, variables, Python functions, <i>etc</i>. The logical operators are "==", "<", "<=", ">", ">=" and "!=" (Not Equal To). If you set the mouse focus at one of the expression boxes and then double-click on the name of one of the output parameters in the list, it will be inserted in that box. Set up the following design objective as shown in the figure below:
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−
<table>
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−
<tr>
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−
<td> [[Image:Picasso L2 Fig6.png|thumb|left|480px|Plots of the magnitude and phase of the S<sub>11</sub> parameter of the patch antenna as a function of frequency.]] </td>
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−
</tr>
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−
</table>
+
  
−
<table>
 
−
<tr>
 
−
<td> [[Image:Picasso L2 Fig7.png|thumb|left|480px|Plots of the real and imaginary parts of the Z<sub>11</sub> parameter of the patch antenna as a function of frequency.]] </td>
 
−
</tr>
 
−
</table>
 
  
−
With [[EM.Picasso]], you can also perform an adaptive frequency sweep of your physical structure. This sweep starts with a few frequency samples in the beginning and then inserts more frequency samples in between and uses a rational function interpolation to achieve a smooth frequency response. Open the frequency sweep settings dialog again and this time choose the radio button '''Adaptive''' for the sweep type. Accept the default values of the adaptive sweep parameters and run and new adaptive frequency sweep simulation of your planar structure. The program may give a warning that during the adaptive sweep, current distribution and far-field radiation pattern data will not be produced. Ignore the warning and continue. Also, after a number of sweep iterations, the program may pop up a message saying the convergence criterion hasn't been met and will ask you whether to continue the sweep process. <u>In that case, reply "No" and stop the sweep</u>. Too many adaptive sweep iterations may sometime lead to spurious spikes in the frequency response.   
+
----
  
−
<table>
+
20*log10(S11M) == -20
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<tr>
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−
<td> [[Image:Picasso L2 Fig10.png|thumb|left|480px|Setting the sweep type to "Adaptive" in the frequency sweep settings dialog.]] </td>
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−
</tr>
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−
</table>
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−
At the end of the sweep simulation, open the data manager and plot the data files "S11_RationalFit.CPX" and "Z11_RationalFit.CPX" in EM.Grid. From the figures below you can clearly see the resonance of the antenna at 2.4GHz. However, the input impedance of the patch antenna at 2.4GHz is about (66 + j99)&Omega;, which is far from an acceptable impedance match.     
+
----
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig8.png|thumb|left|480px|Plots of the magnitude and phase of the S<sub>11</sub> parameter at the end of an adaptive frequency sweep.]] </td>
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<td> [[Image:Picasso L10 Fig5.png|thumb|left|480px|Defining a new design objective in the "Add Objective" dialog.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
 +
 +
Close the "Add Objective" dialog to return to the Objectives dialog. You will see your new design objective added to the current objectives list. Close this dialog, too, and return to the project workspace. 
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig9.png|thumb|left|480px|Plots of the real and imaginary parts of the Z<sub>11</sub> parameter at the end of an adaptive frequency sweep.]] </td>
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<td> [[Image:Picasso L10 Fig6.png|thumb|left|480px|EM.cube's Objective dialog showing the newly defined design objective.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
== Running a Parametric Sweep of the Feed Recess Depth ==
+
== Setting Up the Optimization Process ==
  
−
At this time, you are going to vary the depth of the feed recess to see if it improves the return loss (|S11|). Open the simulation run dialog and select '''Parametric Sweep''' as the simulation mode. You will notice a red box next to the drop-down list. This means that you are not ready to run a simulation because some parameters haven't been set yet.  
+
Open the simulation run dialog and select '''Optimization''' from the drop-down list labeled '''Simulation Mode'''.  
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig12.png|thumb|left|480px|Setting parametric sweep as the simulation mode in EM.Picasso's run dialog.]] </td>
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<td> [[Image:Picasso L10 Fig7.png|thumb|left|480px|Setting optimization as the simulation mode in EM.Picasso's run dialog.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
Click the {{key|Settings}} button next to the '''Simulation Mode''' drop-down list to open the Parametric Sweep Settings dialog.  
+
Click the '''Settings''' button next to this drop-down list to open the Optimization Settings dialog.  
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig13.png|thumb|left|720px|EM.Picasso's parametric sweep settings dialog.]] </td>
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<td> [[Image:Picasso L10 Fig8.png|thumb|left|720px|EM.Picasso's optimization settings dialog before designating the optimization variables.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
On the left side of the dialog you will see a list of all the available independent variables already defined in your project. Select and highlight "recess_dep" and click the right arrow {{key|-->}} button in the middle of the dialog to move the selected variable to the '''Sweep Variables''' list on the right. A new dialog titled "Edit Sweep Variable" opens up. Accept the '''Uniform''' variable type and enter 2, 16, 2, for the start, stop and step values of the sweep variable, respectively. This will create a list of sweep variable values: {2, 4, 6, ..., 14, 16}.  
+
Keep the default optimization '''Algorithm Type''', which is "Powell's Method". Next, you need to define the optimization variables. Similar to the case of a parametric sweep, on the left side of the dialog you will see a list of all the available independent variables already defined in your project. Select and highlight "recess_dep" and click the right arrow {{key|-->}} button in the middle of the dialog to move the selected variable to the '''Optimization Variables''' list on the right. A new dialog titled "Edit Optimization Variable" opens up. Enter 2 and 16 for the minimum and maximum values, respectively. Keep the default '''Variable Precision''' value of 0.1. Similarly, move "recess_wid" to the optimization variables table and enter 1 and 8 for its minimum and maximum values, respectively.  
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig14.png|thumb|left|480px|Setting the bounds and number of samples of the sweep variable.]] </td>
+
<td> [[Image:Picasso L10 Fig9.png|thumb|left|480px|Defining the bounds of the optimization variable "recess_dep".]] </td>
 +
<td> [[Image:Picasso L10 Fig9A.png|thumb|left|480px|Defining the bounds of the optimization variable "recess_wid".]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
Close this dialog and return to the parametric sweep settings dialog. You will see the specifications of the sweep variable in the table on the right.  
+
Back in the optimization settings dialog, you will see the specifications of the two optimization variables in the table on the right. Set the value of '''Max Error''' equal to 0.1. This is used for the convergence of the objective function or error function. You can see from the figure below that the error function or "goal" has been defined by the mathematical expression:
  
−
<table>
 
−
<tr>
 
−
<td> [[Image:Picasso L2 Fig15.png|thumb|left|720px|The parametric sweep settings dialog showing "recess_dep" as the active sweep variable.]] </td>
 
−
</tr>
 
−
</table>
 
  
−
Close the parametric sweep settings dialog and return to the run dialog. Click the {{key|Run}} key to start the parametric sweep. After the completion of the sweep simulation, open the data manager and plot the data file "S11_Sweep.CPX" in EM.Grid. Note that the return loss is minimized for the value recess_dep = 14mm. 
+
----
  
−
<table>
+
| (20*log10(S11M)) - (-20) |  
−
<tr>
+
−
<td> [[Image:Picasso L2 Fig16.png|thumb|left|480px|Plots of the magnitude and phase of the S<sub>11</sub> parameter of the patch antenna as a function of the feed recess depth at f = 2.4GHz.]] </td>
+
−
</tr>
+
−
</table>
+
  
−
== Running a Parametric Sweep of the Feed Recess Width ==
+
----
−
 
+
−
Open the variable dialog and change the value of the variable "recess_dep" to 14mm.
+
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig17.png|thumb|left|480px|Adjusting to the optimal value of the feed recess depth.]] </td>
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<td> [[Image:Picasso L10 Fig10.png|thumb|left|720px|The optimization settings dialog after designating the optimization variables.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
Next, you are going to vary the width of the feed recess to see how far you can improve the return loss (|S11|). Open the simulation run dialog and then the parametric sweep settings dialog. Select and highlight "recess_dep" in the sweep variables table on the right side of the dialog. Click the left arrow {{key|<--}} button in the middle of the dialog to move the selected sweep variable back to the '''Independent Variables''' list on the left. Now, select "recess_wid" from the left table and move it to the right table to make it the active sweep variable. In the "Edit Sweep Variable" dialog, accept the '''Uniform''' variable type and enter 1, 8, 1, for the start, stop and step values of the sweep variable, respectively. This will create a list of sweep variable values. Return to the parametric sweep settings dialog as shown in the figure below.
+
== Running the Optimization of the Patch Antenna ==
  
−
<table>
+
Run the simulation and wait until the optimization algorithm converges. Note that sometimes the optimization process may never converge. This means that the goal you have set for your optimization might never be achieved within the defined range of the optimization variables. In that case, the optimization algorithm will complete the specified maximum number of iterations and will exit the loop. If the optimization is successful, [[EM.Cube]] automatically changes the values of the optimization variables and sets them equal to their optimal values. In this project, the Powell optimization algorithm yields the following optimal values for the designated design variables:   
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<tr>
+
−
<td> [[Image:Picasso L2 Fig18.png|thumb|left|720px|The parametric sweep settings dialog showing "recess_wid" as the active sweep variable.]] </td>
+
−
</tr>
+
−
</table>
+
  
−
Run the new parametric sweep and then plot the data file "S11_Sweep.CPX" in EM.Grid. Note that the return loss is minimized for a value of recess_dep between 2mm and 3mm.
+
{| class="wikitable"
 +
|-
 +
! scope="col"| Design Variable Name
 +
! scope="col"| Optimal Value
 +
|-
 +
| recess_dep
 +
| 13.1384
 +
|-
 +
| recess_wid
 +
| 2.02129
 +
|}
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig19.png|thumb|left|480px|Plots of the magnitude and phase of the S<sub>11</sub> parameter of the patch antenna as a function of the feed recess width (recess_dep = 14mm) at f = 2.4GHz.]] </td>
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<td> [[Image:Picasso L10 Fig11.png|thumb|left|550px|The variables dialog showing the optimal values of the design variables "recess_dep" and "recess_wid".]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
−
 
−
== Analyzing the Patch Antenna with the Optimal Recessed Feed ==
 
−
 
−
You already set the value of the variable "recess_dep" to 14mm in the previous part. Now open the variables dialog again and change the value of the variable "recess_wid" to 2.5mm.
 
  
 
<table>
 
<table>
 
<tr>
 
<tr>
−
<td> [[Image:Picasso L2 Fig20.png|thumb|left|550px|The variables dialog showing the optimal values of the design variables "recess_dep" and "recess_wid".]] </td>
+
<td> [[Image:Picasso L10 Fig12.png|thumb|left|640px|The geometry of the optimized patch antenna with the recessed microstrip feed line.]] </td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
−
After the above changes, your patch antenna structure should look like this:
+
== Verifying Your Optimized Patch Design ==
  
−
<table>
+
To verify the outcome of your optimization process, run a '''Single-Frequency Analysis''' of your patch structure at the project center frequency of fc = 2.4GHz. After the completion of the simulation, the output message window reports the port characteristics of your new optimized antenna: 
−
<tr>
+
−
<td> [[Image:Picasso L2 Fig21.png|thumb|left|640px|The geometry of the patch antenna structure with the optimal recessed feed.]] </td>
+
−
</tr>
+
−
</table>
+
  
−
Run a quick single-frequency PMOM analysis of the optimal structure. At the end of the simulation, the port characteristics are reported as follows:
+
S11: -0.060578 -0.077976j
  
−
S11: 0.011933 +0.142894j
+
S11(dB): -20.109976
  
−
S11(dB): -16.869538
+
Z11: 43.781258 -6.894998j
  
−
Z11: 49.134305 +14.336804j
+
Y11: 0.022288 +0.003510j
  
−
Y11: 0.018756 -0.005473j
+
As you can see from the value of the return loss, the specified design goal has been accomplished.
  
−
The return loss has dramatically improved down to -16.87dB. Visualize the current distribution and 3D radiation pattern of the antenna as shown in the figures below. Notice how the standing wave pattern has diminished on the microstrip feed line due to the improved impedance match. 
+
<p>&nbsp;</p>
 +
[[Image:Top_icon.png|30px]] '''[[#What_You_Will_Learn | Back to the Top of the Page]]'''
  
−
<table>
+
[[Image:Back_icon.png|30px]] '''[[EM.Cube#EM.Picasso_Documentation | Back to EM.Picasso Tutorial Gateway]]'''
−
<tr>
+
−
<td> [[Image:Picasso L2 Fig22.png|thumb|left|640px|The plot of total electric current (JTOT) distribution of the patch antenna.]] </td>
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</tr>
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−
</table>
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−
 
+
−
<table>
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−
<tr>
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−
<td> [[Image:Picasso L2 Fig23.png|thumb|left|640px|The 3D radiation pattern plot of the patch antenna.]] </td>
+
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</tr>
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−
</table>
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−
 
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−
Finally, run an adaptive frequency sweep of your patch antenna with the optimal recessed feed over the frequency range [2GHz, 3GHz]. After the completion of the sweep simulation, open the data manager and plot the data files "S11_RationalFit.CPX" and "Z11_RationalFit.CPX" in EM.Grid. The graphs of the S and Z parameters are shown in the figures below. A very good resonance and impedance match is accomplished at 2.4GHz.
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+
−
<table>
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−
<tr>
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−
<td> [[Image:Picasso L2 Fig24.png|thumb|left|480px|Plots of the magnitude and phase of the S<sub>11</sub> parameter of the patch antenna with the optimal recessed feed.]] </td>
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</tr>
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−
</table>
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−
 
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−
<table>
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−
<tr>
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−
<td> [[Image:Picasso L2 Fig25.png|thumb|left|480px|Plots of the real and imaginary parts of the Z<sub>11</sub> parameter of the patch antenna with the optimal recessed feed.]] </td>
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−
</tr>
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</table>
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<p>&nbsp;</p>
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[[Image:Back_icon.png|40px]] '''[[EM.Cube#EM.Picasso_Tutorial_Lessons | Back to EM.Picasso Tutorial Gateway]]'''
+

Latest revision as of 15:29, 25 June 2019

Tutorial Project: Optimizing A Microstrip Patch Antenna Design
Picasso L10 Fig title.png

Objective: In this project, you will use one of EM.Cube's optimziers to design a patch antenna with a recessed microstrip feed line.

Concepts/Features:

  • Wizard
  • Scattering Wave Port
  • Scattering Parameters
  • Design Variable
  • Design Objective
  • Optimization
  • Error Function

Minimum Version Required: All versions

'Download2x.png Download Link: EMPicasso_Lesson10


What You Will Learn

In this tutorial you will revisit the rectangular patch antenna design with a recessed feed, which you explored earlier in Tutorial Lesson 2. This time, however, you will define a design objective and will use EM.Picasso's optimization utility to optimize the values of designated design variables to achieve your goal.

Back icon.png Back to EM.Picasso Manual

Back icon.png Back to EM.Picasso Tutorial Gateway

Download2x.png Download projects related to this tutorial lesson

Getting Started

Open the EM.Cube application and switch to EM.Picasso. Start a new project with the following parameters:

Starting Parameters
Name EMPicasso_Lesson10
Length Units Millimeters
Frequency Units GHz
Center Frequency 2.4GHz
Bandwidth 0.5GHz

Creating the Patch Geometry with a Recessed Feed

Follow a similar procedure as in Tutorial Lesson 2 and use the Microstrip-Fed Patch Wizard to create the parameterized geometry of a patch antenna with a recessed feed.

The patch antenna geometry with the recessed feed in the project workspace.

Open the variables dialog and make the following changes:

Variable Name Original Definition New Definition
patch_len floor(0.5*lambda0_unit*100/sqrt(er))/100 42
recess_dep 0.015*to_meters 15
recess_wid 0.005*to_meters 5
The variables dialog showing the new definitions of some variables.

Defining the Design Objective

In this project, you will fix the side dimensions of the patch ("patch_len"), and will optimize the two feed variables: "recess_dep" and "recess_wid". But first you need to define a design objective for your project. The goal here is to achieve a good impedance match by varying the design variables. A return loss of -20dB typically represents a very good impedance match.

To define a design objective, click on the Objectives Objective icon.png button of the Simulate Toolbar or select the menu item Simulate → Objectives... EM.Cube's Objectives dialog opens up, which is initially empty.

EM.cube's Objective dialog initially being empty.

Click the Add button of this dialog to open "Add Objective" dialog. At the bottom of this dialog you will see a list of EM.Cube's available standard output parameters. The contents of this list vary depending on the observables you have already defined for your project. Since the wizard created a port definition for this project, you will see a number of standard output parameters related to the S/Z/Y parameters. A design objective is defined as a logical statement:

expression_1 logical operator expression_2

The first and second expressions can be any mathematical expression involving the standard output parameters, variables, Python functions, etc. The logical operators are "==", "<", "<=", ">", ">=" and "!=" (Not Equal To). If you set the mouse focus at one of the expression boxes and then double-click on the name of one of the output parameters in the list, it will be inserted in that box. Set up the following design objective as shown in the figure below:


20*log10(S11M) == -20

Defining a new design objective in the "Add Objective" dialog.

Close the "Add Objective" dialog to return to the Objectives dialog. You will see your new design objective added to the current objectives list. Close this dialog, too, and return to the project workspace.

EM.cube's Objective dialog showing the newly defined design objective.

Setting Up the Optimization Process

Open the simulation run dialog and select Optimization from the drop-down list labeled Simulation Mode.

Setting optimization as the simulation mode in EM.Picasso's run dialog.

Click the Settings button next to this drop-down list to open the Optimization Settings dialog.

EM.Picasso's optimization settings dialog before designating the optimization variables.

Keep the default optimization Algorithm Type, which is "Powell's Method". Next, you need to define the optimization variables. Similar to the case of a parametric sweep, on the left side of the dialog you will see a list of all the available independent variables already defined in your project. Select and highlight "recess_dep" and click the right arrow --> button in the middle of the dialog to move the selected variable to the Optimization Variables list on the right. A new dialog titled "Edit Optimization Variable" opens up. Enter 2 and 16 for the minimum and maximum values, respectively. Keep the default Variable Precision value of 0.1. Similarly, move "recess_wid" to the optimization variables table and enter 1 and 8 for its minimum and maximum values, respectively.

Defining the bounds of the optimization variable "recess_dep".
Defining the bounds of the optimization variable "recess_wid".

Back in the optimization settings dialog, you will see the specifications of the two optimization variables in the table on the right. Set the value of Max Error equal to 0.1. This is used for the convergence of the objective function or error function. You can see from the figure below that the error function or "goal" has been defined by the mathematical expression:


| (20*log10(S11M)) - (-20) |

The optimization settings dialog after designating the optimization variables.

Running the Optimization of the Patch Antenna

Run the simulation and wait until the optimization algorithm converges. Note that sometimes the optimization process may never converge. This means that the goal you have set for your optimization might never be achieved within the defined range of the optimization variables. In that case, the optimization algorithm will complete the specified maximum number of iterations and will exit the loop. If the optimization is successful, EM.Cube automatically changes the values of the optimization variables and sets them equal to their optimal values. In this project, the Powell optimization algorithm yields the following optimal values for the designated design variables:

Design Variable Name Optimal Value
recess_dep 13.1384
recess_wid 2.02129
The variables dialog showing the optimal values of the design variables "recess_dep" and "recess_wid".
The geometry of the optimized patch antenna with the recessed microstrip feed line.

Verifying Your Optimized Patch Design

To verify the outcome of your optimization process, run a Single-Frequency Analysis of your patch structure at the project center frequency of fc = 2.4GHz. After the completion of the simulation, the output message window reports the port characteristics of your new optimized antenna:

S11: -0.060578 -0.077976j

S11(dB): -20.109976

Z11: 43.781258 -6.894998j

Y11: 0.022288 +0.003510j

As you can see from the value of the return loss, the specified design goal has been accomplished.

 

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