Chapter 5 Current and Pattern Display, Electromagnetic Optimization We have discussed basic technique and geometry construction in the last two chapters. We have used the MGRID, IE3D and MODUA for construction, simulation and display in chapters 3 and 4. In this chapter, we will discuss the use of MGRID and PATTERNVIEW for the current and pattern display. Before the IE3D 9.0, we have been using the CURVIEW application program to perform current distribution, pattern calculation and display. The PATTERNVIEW was implemented later for pattern display, comparison and processing. PATTERNVIEW is certainly better than the CURVIEW in pattern display. Starting from IE3D 9.0, for better integration, we have implemented all the features of CURVIEW into the layout editor: the MGRID. All the current distribution and pattern handling features are enhanced on the MGRID. The CURVIEW is completely replaced, even though it may still be offered in the IE3D 9.0. The CURVIEW should be phased out after the version 9.0 and we will not document its usage here. The old users are suggested to switch to MGRID and PATTERN for current and pattern handling. In order to display the current distribution and radiation patterns of a structure, we need to run a simulation on the structure and save the current distribution data file and pattern data file. Our first example is the spiral inductor we built in Chapter 4. Section 1. Simulation of a Spiral Inductor and Extraction of L and Q. Step 1 Run MGRID. Open c:\ie3d\practice\cspiral1.geo. Select Simulate in Process menu. Response: The Simulation Setup dialog comes up. Step 2 We want to sweep a wide frequency range and see how the frequency response looks like. Enter Start Freq = 0.05 GHz, End Freq = 10 GHz, Number of Freq = 200. Hit Enter key. Response: 200 frequency points starting from 0.05 GHz to 10 GHz with step 0.05 GHz are entered in the list.
Transcript
Chapter 5 Current and Pattern Display, Electromagnetic Optimization
We have discussed basic technique and geometry construction in the last two chapters. We have used the MGRID, IE3D and MODUA for construction, simulation and display in chapters 3 and 4. In this chapter, we will discuss the use of MGRID and PATTERNVIEW for the current and pattern display.
Before the IE3D 9.0, we have been using the CURVIEW application program to perform current distribution, pattern calculation and display. The PATTERNVIEW was implemented later for pattern display, comparison and processing. PATTERNVIEW is certainly better than the CURVIEW in pattern display.
Starting from IE3D 9.0, for better integration, we have implemented all the features of CURVIEW into the layout editor: the MGRID. All the current distribution and pattern handling features are enhanced on the MGRID. The CURVIEW is completely replaced, even though it may still be offered in the IE3D 9.0. The CURVIEW should be phased out after the version 9.0 and we will not document its usage here. The old users are suggested to switch to MGRID and PATTERN for current and pattern handling.
In order to display the current distribution and radiation patterns of a structure, we need to run a simulation on the structure and save the current distribution data file and pattern data file. Our first example is the spiral inductor we built in Chapter 4.
Section 1. Simulation of a Spiral Inductor and Extraction of L and Q.
Step 1 Run MGRID. Open c:\ie3d\practice\cspiral1.geo. Select Simulate in Process menu.
Response:The Simulation Setup dialog comes up.
Step 2 We want to sweep a wide frequency range and see how the frequency response looks like. Enter Start Freq = 0.05 GHz, End Freq = 10 GHz, Number of Freq = 200. Hit Enter key.
Response:200 frequency points starting from 0.05 GHz to 10 GHz with step 0.05 GHz are entered
in the list.
Step 3 It is not suggested to enable Current Distribution File for so many frequency points. Otherwise, the file will be big. We want to check the frequency response first. Select Adaptive Intelli-Fit (AIF). Uncheck Current Distribution File. The Radiation Pattern File will be automatically un-checked when we un-check the Current Distribution File. Disable Automatic Edge Cells (AEC). AEC is good for high accuracy results. However, it will slow down the simulation. Here, we just want to have some fast results. Select OK to continue.
Response:The MGRID will display a dialog “Errors or Warnings Detected in Port Validation”
(see Figure 5.1).
Explanation:Ports are the most difficult topics for a general user of non-Electromagnetic simulation
expert to manage. Starting from the IE3D 9.0, we try to implement some validation routine to validate the ports and give suggestions to the users before a simulation. Discussions on the port validation errors and warnings are documented in the Table 5.1.
Step 4 There are “High Warning”s on both ports 1 and 2. However, if you check the “v1. vs. v2” statements in the descriptions, you will see that the v1 and v2 are not very far away. For the 1 st
statement in description list box in the dialog, you will see “… is too big (0.108909 vs. 0.085)”. It indicates that the substrate thickness is about 20% thicker than the warning limit. It is not too much. For this spiral example, the 20 mils out of 21 mils in the substrate is some conductive material. The insulation layer is just 1 mil thick. The “effective” distance between the trace and the ground should be smaller than 21 mils due to the conductivity. It should not be so serious. Please select CONTINUE to start the simulation.
Figure 5.1 The warnings issued in port validation by MGRID.
Table 5.1 The classification of error or warning messages on port validation on MGRID.Error/Warning Seriousness Description
Error Very Serious The users should try to fix the problem before he can do the simulation.
High Warning Quite Serious Normally, it is quite serious. However, the user should check the statement (v1. vs. v2) in the description of the item. If the values of v1 and v2 are close, it should not be a big problem.
Medium Warning Somewhat Serious It is not as serious as the High Warning. You should also check the statement (v1. vs. v2) in the description.
Low Warning Not Serious It should not be very serious warning. However, it is possible it may cause accuracy problem.
Notes: It is impossible for MGRID to detect all the possible problems for you; Some detected problems may not be as serious as MGRID may think; It does not mean that your circuit is ok if MGRID did not issue any warning.
Response:IE3D will be invoked and it will take less than 1 minute to simulate the structure on
modern PC. After the simulation, MODUA is invoked to display the s-parameters. It can be in either Cartesian coordinate or Smith Chart form.
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Step 5 If the display is not the s-parameters in Cartesian coordinate, you can select “Define Display Graph” in Control menu of MODUA. Select “dB and Phase of S-Parameters”. Select OK to continue. Select “dB[S(1,1)]” and “dB[S(2,1)]”. Then, select OK to display the s-parameters in Cartesian coordinate (see Figure 5.2).
Figure 5.2 The frequency response of the spiral inductor.
Explanation:It is a typical spiral inductor’s response. The S21 is close to 1 (or dB[S21] is close to 0
dB) at DC and decreasing with frequency. The S11 is increasing with frequency. Due to the lossy substrate, the S11 cannot go up to the 1. Some users may be interested in the L and Q-values of the inductor. The simple equivalent circuit of the spiral inductor is an L and an R in series. However, a user should understand it is just a very low frequency approximation. The wide-band equivalent circuit is far more complicated than even usually used and more complicated -network. In our calculation, the Q-value is calculated as the Im(Zin)/Re(Zin) when the spiral is fed as a 1-port differential feed. It may be different from other more precise model. On the IE3D, we do allow the extraction of L and Q even though we know the values are no longer meaningful at high frequency.
Step 6 Select LC-Equivalent in Process menu. Select OK for the Multiple Frequency LC-Equivalence dialog. Select “With Shunt R” for the Shunt R Option in Port Definition Style for Equivalence dialog. Select OK to continue. MODUA will start the extraction for you. It will issue a warning on negative inductance. It is due to the fact that the equivalent circuit is no longer valid at some high frequency. If we enforce the equivalence, we will get negative L-value. Select YES to continue. MODUA will finish the extraction in one minute. After it finishes, it will issue a message stating that the results are saved into a file called: cspiral1.txt. Select OK to continue. The spiral1.txt file will be opened on the NOTEPAD accessory of Windows.
Explanation:Part of the low frequency data is listed in Table 5.2. We can import the data into
Microsoft Excel or similar application programs to plot the curves. Figure 5.3 shows the L and Q-values vs. frequency plotted on Microsoft Excel. As you can see, the L-values decreases
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and eventually goes below 0 at about 1.5 GHz, meaning that the equivalent circuit is no longer valid at 1.5 GHz. In fact, the circuit is no longer accurate beyond about 0.25 GHz. It is indicated by the Error Factor (see Table 5.2). From our experience, when the Error Factor exceeds 0.25-0.3, the equivalent circuit will depart from the original s-parameters.
In case we want to obtain the LC-equivalent circuit compatible with SPICE format. We should perform the extraction at one single frequency only. MODUA will extract the equivalent circuit at the frequency. The user can save the extracted results into SPICE format by selecting the Save SPICE File in FILE menu of MODUA.
Table 5.2 The LC-equivalent circuit parameters at low frequency.
Freq (GHz) Error Factor Q-Factor Series R (Ohms) Series L (nH) Shunt R (Ohm)Shunt C (pF)
Step 1 Save the opened file c:\ie3d\practice\cspiral1.geo as c:\ie3d\practice\cspiral1a.geo. Select Simulate in Process menu.
Explanation:This time, we want to simulate it as selected frequency points with Current Distribution
File saved.
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Step 2 Select Delete All in the Frequency Parameters group to remove all the frequency points. Enter Start Freq = 0.5, End Freq = 2 and Number of Freq = 4. Hit Enter key.
Response:The 4 frequency points: 0.5, 1.0, 1.5, 2.0 are entered into the list.
Step 3 Enter Start Freq = 5 and hit Enter.
Response:The f = 5 GHz is also entered into the list.
Step 4 Uncheck AIF, Check Current Distribution File. Select OK to continue. MGRID will issue the warnings again. Select Continue to start the simulation. The simulation will be done in a short time.
Response:After the simulation, MODUA is invoked to display the s-parameters. Another MGRID
is invoked for meshed structure and current distribution display.
Explanation:Before the version 9.0, CURVIEW is used for the post-processing display of the
meshed structure and current distribution display. For better integration of the package, the features of CURVIEW have been completely integrated into the MGRID.
The display on the meshed structure is very similar to the display of original structure. The meshed structure is shown in the main window of MGRID as top view, and in the 3D view window. In fact, for the post-processing, the 3D view window is the main display window. There is another window showing the layers of the meshed structure. This window is also used to show the color bars for current display.
The users may find that menus on the MGRID main window are changed. The users can no longer use all the editing features of MGRID except the users can still select polygons and vertices.
Step 5 Please press down the left mouse button on the 3D view and move. The 3D view of the spiral will change angles. Please hit any of the following 6 keys: ←, ↑, →, ↓, Home, End. You will see the view angles are also changed. To zoom the view, press down the “Ctrl” key and window the portion you want to view. To pan the window, press down the right mouse button on the 3D view and move. Use the above commands to adjust the 3D view to appropriate angles and size.
Step 6 Select Display Current Distribution in Process menu of the MGRID main window.
Response:The Current Distribution Display Parameters dialog is shown in Figure 5.4.
Explanation:You can select the types of display on the combo box on the top left. The default is
Average Current Distribution. At the time of this writing, there are 6 types of displays for you to select. They are documented in Appendix L. The listbox on the left lists all the 5 frequency points. A user must choose one frequency once at a time.
On the right hand side of the listbox, a user can choose the parameters for the control of the display. For example, a user can choose to display electric current or magnetic current.
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The user can choose whether he wants to display the boundaries of each cell. The user can choose to use dB or linear for the scaling of the color.
The lower left corner lists the layers of the structure. A user can choose which layers will be displayed. The lower right corner lists the ports and excitations. The user can choose the source type: (1) Voltage Source, (2) Current Source, and (3) Wave Source. The user can also define the magnitude and phase of the source, and the terminating impedance of each port. Please read Appendix R for the meaning of the different sources.
Figure 5.4 The Current Distribution Display Parameters dialog.
Step 7 Select OK to accept the default settings for the Current Distribution Display.
Response:The 3D view is updated with colorful display. A new window showing the port
excitation appears (see Figure 5.5).
Explanation:The spiral becomes red color. The color window shows a color bar for the scaling of the
colors. Different colors at different locations of the spiral indicate the current magnitudes are different. In fact, at the low frequency of 0.5 GHz, the color is always red on the spiral, indicating that the current density does not change much on the whole spiral.
The Excitation window shows the sources magnitude and phase, the incident wave, reflected wave, voltage, current and terminating impedance at each port. The incident and reflected waves are always referenced to the 50-ohm system.
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What is shown in Figure 5.5 is the average current distribution. For more information on average current distribution, please read the Appendix L.
Figure 5.5 Nearly uniform current distribution on the spiral at low frequency (0.5 GHz).
Figure 5.6 Significantly non-uniform current on the spiral at high frequency (5 GHz).
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Step 8 Select Display Current Distribution in Process menu of the MGRID main window again.
Response:The Current Distribution Display Parameters dialog comes up again.
Explanation:This time, the Auto Color Scaling is automatically un-checked. The Max E-Current is
329.81. This is the maximum electric current density detected at 0.5 GHz for the last display. It was the reference for 0 dB in the last display. It may not be the maximum electric current for other frequencies. However, for comparison, we will not change it for the display of other frequency points. If you want to get the maximum electric current density at a specific frequency point, you should check Auto Color Scaling for each frequency’s display.
Step 9 Select “Freq = 5 GHz” in the frequency listbox. Select OK to continue.
Response:The 3D view is updated. We will see more different colors on the spiral (Figure 5.6).
Explanation:At higher frequency, the current will become more distributive. The more colors on the
spiral indicate that the current is stronger at some locations than at other locations. If we want to distinguish the colors more, we can select the Display Current Distribution menu item again, and change the “Mag Scale” and “dB Step” values. We will not do it here. Interested users can try it out.
Section 3. Vector Current Display.
What are shown in Figures 5.5 and 5.6 are the average current distribution. It indicates where the current are strong or weak as a time average value. However, we cannot get the direction of the current at specific locations. As it is discussed in Appendix L, in the frequency domain, current distribution is a complex vector function. In the other word, the direction of the vector is normally time varying. Therefore, it is meaningless to display the time average vector current. Instead, we will be interested in the vector current at specific locations at different times. From the directions at specific times, we will know the polarization properties of antenna structures. We will demonstrate how we can display the vector current at a specific time.
Step 1 Select Display Current Distribution in Process menu of the MGRID main window again.
Response:The Current Distribution Display Parameters dialog comes up.
Step 2 Select Vector Current Display in the combo box at the upper left corner (see Figure 5.7). Make sure the frequency is 5 GHz.
Explanation: You may find that there are a few parameters activated: (1) Vector Shape, (2) Vector
Size, and (3) Cycle Count. On the vector current display on the CURVIEW, the size of the vectors indicates the magnitude of the current density at a specific location at a specific time. It is realized that the magnitude of current density may differ in a few orders at different locations. The difference of orders may cause huge difference in the vector size. On the MGRID, we implement a better scheme with same size of vectors. The magnitude of the current density is represented by the colors of the vectors in terms of dB.
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The vectors on MGRID are cone shaped vectors. The parameter of Vector Shape defines the ratio of the diameter of the cone bottom circle over the length of the cone. Its default value is 0.5. The parameter of Vector Size defines the size of the vectors. Its default size is calculated automatically based upon the size of the meshing. The Cycle Count defines the display time. What we are simulating is the frequency domain response of the current distribution. The current will be changing as the sine function of time and frequency. In some sense, when we display the vector current distribution in time, we only need to display them at some fractions of a cycle. The Cycle Count that takes the value from 0 to 1 defines the time in a cycle.
Figure 5.7 The dialog after Vector Current Distribution is selected.
Step 3 Make sure the parameters are like what are shown in Figure 5.7. Select OK to continue. The Vector Current Distribution will be shown.
Step 4 You can see the vectors are pointing at the directions of the trace, as expected. The color of the trace is in uniform brown color. The colors of the vectors are changing, indicating the strength of the current at different location at the time of 0.25 cycle. Select Display Current Distribution in Process menu again. Change the Vector Size to 2 mm.
Response:The size of the vectors is increased and shown in Figure 5.8.
Step 5 Select Current Distribution Display in Process menu. Change the Cycle Count from 0.25 to 0.5. Select OK to continue.
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Response:The colors of the vectors are changed indicating the change of vector current
distribution at different time.
Figure 5.8 The Vector Current Display at 0.25 cycle at 5 GHz.
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Figure 5.9 The Vector Current Display at 0.5 cycle at 5 GHz.
Section 4. Average and Vector Current Display.
We have shown how to display the average and vector current distribution. Either display reveals some specific information of the current distribution on the structure. Can we display the information simultaneously on one single display? It was not ok on the CURVIEW. However, we have implemented such a feature on the MGRID 9.0.
Step 1 Select Display Current Distribution in Process menu of MGRID. MGRID will prompt you for the display parameters. Select Average and Vector Current Distribution for the display type in the combo box in the upper left corner. Select OK to continue.
Response:The view of the current distribution on the spiral is changed again. We will see different
colors on the structures indicating the average current distribution on the structures. We will also see vectors of different colors indicating the strength of current at a specific time. The color of the structure and the color of vector at a specific location do not necessary to be the same. Apparently, at a specific location, the average current can be a large value. However, it may not be necessarily large at a specific time.
Step 2 Select the Display Current Distribution in Process menu again. Change the Cycle Count to other values. You will see the colors at different locations of the structure do not change. However, the colors of the vectors are changing with the Cycle Count. The colors of the structure indicate the average magnitude of the current at different locations. They are not functions of time. The colors of the vectors indicate the magnitude of the current at different locations at different times. They are functions of time.
Section 5. Scalar and Vector Current Distribution Animation.
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As we can see, the current distribution on the structure is a function of time. We can animate how the current is flowing on the structure.
Step 1 Select Display Current Distribution in Process menu of MGRID. MGRID will prompt you for the display parameters. Select Scalar Current Distribution Animation for the display type in the combo box in the upper left corner.
Response:The Current Distribution Display Parameters dialog is changed. You will see the two
parameters are activated: (1) Frames / Cycle and (2) Interval (ms). The default value of Frames / Cycle is 15, meaning that the MGRID will animate the current at the rate of 15 frames per cycle. The Interval (ms) is 200 ms, which means that the time interval between two consecutive frames is 200 ms. Each cycle will take 3000 ms or 3 seconds.
Step 2 Change the Frames / Cycle to 15 and Interval (ms) to 100 ms. Select OK to continue.
Response:We will see the colors at different locations of the structure are changing with time.
Explanation:Unlike the colors in the average current display, the colors in this display represent the
strength of the current at a specific location at a specific time. It has the same meaning as the colors of the vectors in the vector current display. The changing colors on the structure indicate the flow of current as a function of time.
Step 3 Select Display Current Distribution in Process menu again. Select Vector Current Distribution Animation for the display type in the combo box in the upper left corner. Select OK to continue.
Response:The current is animated with vectors of changing colors.
Explanation:The changing colors of the vectors indicate both the magnitude and direction of the
current flow as functions of time.
Section 6. Using ZDibAnimator for Current Animation.
The ZDibAnimator was first developed for near field animation on the FIDELITY Electromagnetic Simulator, a non-uniform FDTD full 3D simulator from Zeland Software, Inc. Although it had been enabled for the IE3D users, it was of little use until we released the IE3D 9.0. On the IE3D 9.0, we can perform high quality current distribution animation on the MGRID 9.0. However, we can also get high quality current animation on the ZDibAnimator. The animation on MGRID and the animation on ZDibAnimator have their own advantage. The MGRID 9.0 is a real-time animation. It does not need to create bitmap files that may take large amount of hard disk space. The users can change the parameters of the animation real time. The disadvantages of animation on MGRID are: (1) The user needs to adjust the parameters to get a color animation; (2) It may be difficult to reproduce the same meaningful display; (3) When the number of polygons is large, the display quality may be lowered.
On the other hand, a user can capture the bitmap files for some carefully adjusted animation. They can re-produce the animation exactly any time later as long as they save the bitmap files on the ZDibAnimator. The quality of the animation on the ZDibAnimator will be the same no matter how many polygons are in the display. The disadvantage of animation on ZDibAnimator is that we cannot change its
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parameters during the animation. If we want to get the animation with different parameters, we have to produce multiple sets of bitmap pictures. Normally, each set of bitmap pictures contains about 10 to 50 frames. Each frame may take more 1 MB hard disk space. They may occupy large amount of hard disk space. We will demonstrate how we can use the ZDibAnimator for current distribution animation.
Step 1. While the MGRID is still displaying the vector current animation, select the Save to Bitmap Files in the View menu of the 3D view window (not the main window) of MGRID.
Response:MGRID will prompt you the dialog for saving the bitmap files (see Figure 5.10).
Step 2 Check the Invoke ZDibAnimator for Animation. Select OK to continue.
Explanation:A user can enter a name prefix for the bitmap files. Here, we just accept the default
prefix. Please take a note on which directory the bitmap files are located. If you open the cspiral1a.cur file from c:\ie3d\practice directory, the bitmap files should be located at c:\ie3d\practice directory.
Response:The MGRID will save the bitmap files. After it saves all the files. It will prompt you
that the files are saved.
Step 3 Select OK to continue.
Response:The ZDibAnimator is invoked for animation. The animation on MGRID is still going
on. The quality of the two animations should be the same.
Figure 5.10 The dialog for saving bitmap files for animation on ZDibAnimator.
Step 4 Close the ZDibAnimator. We are going to show you how to use the ZDibAnimator to re-produce the exact animation using the saved bitmap files.
Step 5 Run the ZDibAnimator from Zeland Program Manager or Zeland Folder. 5-13
Response:A dialog will come up and ask you for the Bitmap Options.
Explanation:The default Animation Time Interval is 100 ms and it is a good setting. The next step is
to select the files.
Step 6 Select Browse button. You will be prompted to select the bitmap files. Change the directory to: c:\ie3d\samples or whatever directory where the saved bitmap files are. We will see a list of bitmap files in the directory. You need to select a group of them. For our case, we have the list shown in Table 5.3.
Table 5.3 The bitmap files in the listCspiral1a_0.bmp Cspiral1a_14.bmp Cspiral1a_7.bmpCspiral1a_1.bmp Cspiral1a_2.bmp Cspiral1a_8.bmpCspiral1a_10.bmp Cspiral1a_3.bmp Cspiral1a_9.bmpCspiral1a_11.bmp Cspiral1a_4.bmpCspiral1a_12.bmp Cspiral1a_5.bmpCspiral1a_13.bmp Cspiral1a_6.bmp
Explanation:The bitmap files are in numerical order according to the first digit of the counting
number. So, the 1st bitmap file is the cspiral1a_0.bmp. The last bitmap file is the cspiral1a_9.bmp instead of the cspiral1a_14.bmp. It is not critical. We should select all the 15 files.
Step 7 Click at the cspiral1a_0.bmp file in the list to select it. Press down the “Shift” key and select the cspiral1a_9.bmp file. All the 15 bitmap files in the range should be selected. Click Open button.
Response:All the 15 bitmap files should be selected into the listbox in the “Please Specify Bitmap
Options” dialog (see Figure 5.11).
Explanation:All the files should be automatically ordered. We have not seen any case of disorder. In
case a user encounters such a case, he can always select a file in the list. Then, he can select the Up and Down button on the upper right of the listbox to adjust the order of the files.
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Figure 5.11 The “Please Specify Bitmap Options” in ZDibAnimator after the files selected.
Step 8 Select OK to continue. The ZDibAnimator will be up and display the animation of the spiral. It should be exactly the same as the one we invoked in step 3 of this section. A user can select the Time Interval in the View menu of ZDibAnimator to change the speed of the animation. No other parameters can be changed in the ZDibAnimator.
Step 9 The user can play with the animations on both the MGRID and ZDibAnimator to see compare the advantage of animation in either applications. On the MGRID, there is another animation option: Scalar and Vector Current Distribution Animation. In fact, if you choose it, you may not see any difference between it and the Scalar Current Distribution Animation. The reason is that the colors at a specific location are the same as the colors of the vectors. They both represent the current at the location at a specific time. We may not be able to distinguish the vectors from the structure.
Step 10 Close the ZDibAnimator.
Step 11 Select Display Structure in Process menu of MGRID. Select OK to continue. MGRID will display the structure in different colors, indicating the cells on different layers. Our next step is to show other features in the next section.
Section 7. Save Current Distribution Data into ASCII File.
Some users may be interested in the current density values on the structure. The IE3D 9.0 allows access of such data.
Step 1 Select Display Current Distribution in Process menu. Select Average Current Distribution from the combo box. Select OK to continue.
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The MGRID is displaying the average current distribution again.
Step 2 Select Save Current Density Data in the File menu of MGRID. The MGRID will prompt you for the data file name. The default name is: c:\ie3d\practice\cspiral1a_5.cdd. Select OK to continue.
Response:The current distribution data is saved into an ASCII file.
Explanation:The ASCII file is very simple to understand. It lists the number of cells. Then, it will
list how many vertices a cell has, whether a cell is selected, the vertices of the cells, and the current density at each vertex of the cell. Interested users can try to check the data.
Section 8. Radiation Pattern and Loss Calculation.
For an antenna designer, he may not only be interested in the current distribution, he may also want to know the radiation pattern of an antenna. For a circuit designer, he may be concerned about how much radiation or emission his circuit may cause. He may also want to know where the loss goes. For a general structure, the involved losses are described in Table 5.4.
Table 5.4 The different losses involved in an electrical structure in open environment.Type Description
Metallic Loss It is the loss consumed on the conductors of the structure.Dielectric Loss It is the loss consumed in the layered substrates.
Surface Wave Loss It is the loss of the radiated field along the surface of the substrate layers. The field strength is proportional to 1/, where is the radius of the cylindrical coordinate system.
Radiation Loss It is the loss of the radiated field in the open space. The field strength is proportional to 1/r, where r is the radius of the spherical coordinate system.
In a practical system, there is always dielectric loss on each substrate no matter how small the loss is. In such a case, the surface wave will eventually be absorbed by the substrates, and the surface wave field strength will be decaying exponentially instead of 1/. The metallic loss, the dielectric loss and surface wave loss can be considered as material loss. Therefore, we can consider the loss as the sum of material loss and radiation loss.
On the IE3D, we will be able to predict the material loss and the radiation loss. However, we will not be able to separate the metallic loss, dielectric loss and surface wave loss. To predict the losses, we need to perform a pattern calculation.
Step 1 While the cspiral1a.cur file is still opened on MGRID, select the Pattern Calculation in Process menu of MGRID.
Response:The Pattern Calculation Information dialog comes up.
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Figure 5.12 The Pattern Calculation Information dialog when selected the 1st time.
Explanation:Pattern calculation used to be on CURVIEW before the IE3D 9.0. Starting from IE3D
9.0, we are able to perform pattern calculation on MGRID and IE3D. In this example, we will demonstrate how we can calculate the pattern from the .CUR file on MGRID. In fact, when we setup the simulation on MGRID for the IE3D, we can choose Radiation Pattern File option in the setup dialog. When we choose this option, IE3D will perform the pattern calculation automatically. Such an option was available on earlier version of MGRID before version 9.0. The corresponding IE3D will also perform the pattern calculation automatically when we enable the option on earlier version of the MGRID. However, the earlier version of IE3D does not do the pattern calculation by itself. Internally, it will invoke the CURVIEW to do the calculation transparently. Starting from the IE3D 9.0, a user can perform the pattern calculation on either MGRID or IE3D using the same routine internally. A user should understand that the patterns calculated on the IE3D and MGRID may be slightly different from those on the CURVIEW for some structures. There are two reasons: (1) The pattern calculations on IE3D and MGRID may use higher accuracy floating point numbers in the calculation. (2) There are improvements and bug fixing on the IE3D and MGRID for pattern calculation.
On the dialog, the Perform New Pattern Calculation is checked. However, it is grayed out. The source portion is also grayed out too. This is the 1 st time the Pattern Calculation command is applied; we will always have such a setting. We can add more angles into the Elevation Angle (Theta) and the Azimuth Angle (Phi). The pattern calculation will be
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performed on all the frequency points. The pattern calculation will be performed with all the different combinations in the excitation. We do not need to worry about the excitations and terminations on the ports right now.
Step 2 Select OK to continue.
Response:MGRID will start the pattern calculation for the frequency response. After it finishes, it
will prompt the user that the “General Pattern Calculation Finished. The user can choose Define or Continue option.
Explanation:If a user choose Continue option, MGRID will go back to the display before the user
choose the Pattern Calculation command. However, the calculated pattern data will be saved in the memory. As long as the user is still displaying this structure, he can still process the pattern data by select the Pattern Calculation command in Process menu of MGRID.
If a user wants to process the pattern directly, he should choose the Define button.
Step 3 Select Define button.
Response:The Pattern Calculation Information dialog comes up again. However, it is different
from the 1st time (see Figure 5.13).
Explanation:The Pattern Calculation Information dialog shown in Figure 5.13 is after a pattern
calculation is performed. In fact, if a user chose Continue in Step 3, then he chose Pattern Calculation in Process menu, he will get the same window.
This time, the pattern is calculated. The Perform New Pattern Calculation is un-checked. However, it is activated for selection. The angles are grayed out. The default setting for the dialog is to define and save the pattern with the specified excitation and termination at each port. A user can specify the excitations and terminations as he like. The MGRID will find the pattern with the specified excitations and terminations easily and save it into the file name specified in the upper portion of the dialog.
Old IE3D users will remember that the pattern calculation on CURVIEW is based upon the excitation and termination. When a user tries to calculate the pattern, the CURVIEW will ask for the excitation and termination. In this way, the pattern will be calculated again and again for every different combination of excitations and terminations. On the MGRID 9.0, the pattern calculation is separated into 2 steps: (1) The 1 st step is to find the general pattern with some number of combinations of excitations and terminations. (2) The 2nd step is to specify the excitations and terminations to find the pattern of specified conditions. The 1 st step takes about the same time or longer time than the CURVIEW’s way. However, the 2nd step takes no time. It will save much computational effort if many different combinations of excitations and terminations are needed. In fact, the new way in MGRID 9.0 is basically the functionality of tuning. After the 1st step of pattern calculation, we can specify the combination of excitations and terminations and find its results in real-time. Further development on this feature will be the optimization of excitations and terminations of an antenna array. This feature should be implemented soon after the release of IE3D 9.0.
Normally, a user does not need to choose Perform New Pattern Calculation unless he needs the pattern with more theta and phi angles. If he chooses Perform New Pattern Calculation, he will get the same dialog shown in Figure 5.12.
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Figure 5.13 The dialog when the pattern is calculated.
Step 4. Make sure the Invoke checkbox is checked. Select OK to continue.
Response:The pattern with the default specified excitations and terminations are saved into: c:\
ie3d\samples\cspiral1a.pat file. The PatternView is invoked and the cspiral1a.pat file is added into the list for pattern display.
Explanation:Automatically invoking PatternView for pattern display is also a new feature for the
IE3D 9.0. The PatternView’s main window is a listbox. It allows a user to add a list of patterns into the listbox for comparison or post-processing. In the IE3D 9.0, we allow the MGRID to invoke PatternView and add the calculated pattern into Patternview automatically. The PatternView should be ready for the user to display the calculated pattern.
If we did not choose the Invoke option, the pattern will be saved and the PatternView will not be invoked. We need to run the PatternView; select the Add Pattern in Edit menu of PatternView to add the cspiral1a.pat file into the list.
Section 9. Pattern Properties.
Step 1 Make sure the pattern list is the activated window, select the Pattern Properties in Edit menu.
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Explanation:On the PatternView, we can display the 3D pattern and the 2D patterns in multiple
windows. For different types of windows, the menu on the PatternView will be differently. If we want to check the Pattern Properties, we need to make sure the pattern list window is activated.
Response:A new dialog is created listing the selected pattern’s properties at different frequency
points in a listbox (see Figure 5.14).
Explanation:A user can scroll the listbox to get the different data. If a user wants to get more
information displayed, he can select View in Browser button. The Internet Explorer or the default web browser of your computer will be invoked to display the pattern properties. For our example, the pattern properties at 0.5 GHz and 5 GHz are listed in Table 5.5.
As you can see from Table 5.5, the radiated power is increased substantially from 0.5 to 5 GHz. Due to the difference in the input impedance at different frequency points, the Input Power is different even though the Incident Power is the same. A user should understand that the Input Power in this 2-port example is the net input power from the 2 ports. For our case, the port 1 is excited and the port 2 is terminated with 50-ohms. Large amount of power is consumed at the load at the port 2. The power consumed at the port 2 is considered as negative value in the net input power. We can derive the different powers and losses from Table 5.5. The derived powers and losses are documented in Table 5.6. Apparently, the radiation loss is very small. The majority loss is the material losses (metallic loss, dielectric loss and surface wave loss). In fact, majority of the material loss is from the loss of power on the finite conductivity layer or the layer from 0 to 20 mils. The real substrate is from 20 to 21 mils. It is just 1 mil thick. It does not excite much radiation.
Step 2 Select OK to continue. The Pattern Properties dialog will be closed. A user can select the menu items in the Display menu of PatternView to display the 2D and 3D patterns and the pattern parameters vs. frequency plots. We will not show the steps in this example. Interested users can explore the rich functionality of the PatternView in display and handling. We will discuss the pattern display in the next example on antenna modeling.
Section 10. A Typical Antenna Modeling Example.
For antenna users, radiation patterns will be of great interest. Here, we will demonstrate a simple example for antenna modeling. The antenna we are going to demonstrate is an edge fed rectangular patch antenna with inset. The top view is shown in Figure 5.14. The parameters of the antenna are shown in Table 5.7. The question is how we can build the antenna. We will show you how you can use the efficient commands on the IE3D to build the structure in just a few steps.
Step 1 Run MGRID and open the file: c:\ie3d\samples\rpatch1.geo. It is the exact structure we want to simulate. We will not show how to enter the Basic Parameters in Param menu. We will re-build the polygons to show you the procedure.
Table 5.5 The pattern properties at 0.5 GHz and 5 GHz.File Name C:\ie3d\practice\cspiral1a.patPattern ID
Port Number2
Frequency 0.5 (GHz) 5 (GHz)Incident Power 0.01 (W) 0.01 (W)
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Input Power 0.000817417 (W) 0.00764728 (W)Radiated Power 8.35253e-011 (W) 1.48793e-007 (W)
Average Radiated Power 6.64673e-012 (W/s) 1.18406e-008 (W/s)Radiation Efficiency 1.02E-05% 0.00195%Antenna Efficiency 8.35E-07% 0.00149%Linear Properties
Linear Gain -75.808 dBi -42.9998 dBiLinear Directivity 4.97382 dBi 5.27442 dBiLinear Maximum at (5, 200) deg. at (10, 240) deg.3dB Beam Width (84.9398, 174.71) deg. (82.6039, 170.665) deg.
LH Circular PropertiesCircular Gain -78.4739 dBi -43.8052 dBi
Circular Directivity 2.30793 dBi 4.46902 dBiCircular Maximum at (10, 20) deg. at (10, 250) deg.3dB Beam Width (84.7121, 174.312) deg. (73.124, 156.574) deg.
No. 1 PortVs=2/0 (V), Zs=(50,0) Ohms,
Zc=(50,0) OhmVs=2/0 (V), Zs=(50,0) Ohms,
Zc=(50,0) OhmV=1.38/14.3 (V),
I=0.0150/-27.0 (A)V=1.29/-6.81 (V), I=0.0147/12.0
(A)Inc=1/-1.59e-015 (V), Ref=0.476/45.5 (V)
Inc=1/3.90e-014 (V), Ref=0.320/-28.5 (V)
No. 2 PortVs=0/0 (V), Zs=(50,0) Ohms,
Zc=(50,0) OhmVs=0/0 (V), Zs=(50,0) Ohms,
Zc=(50,0) Ohm
V=0.832/-43.6 (V), I=0.0166/136.4 (A)
V=0.364327/139.315 (V), I=0.00728654/-40.6849 (A)
Inc=3.13e-015/64.8 (V),
Ref=0.832/-43.6 (V)Inc=1.32e-015/49.3 (V),
Ref=0.364/139.3 (V)
Table 5.6 The powers and losses at 0.5 GHz and 5 GHz. The “*” – indicates the quantity calculated based upon the parameters in Table 5.5.
Frequency 0.5 (GHz) 5 (GHz)Incident Power 0.01 (W) 0.01 (W)
Input Power 0.000817 (W) 0.00765 (W)Radiated Power 8.35253e-011 (W) 1.48793e-007 (W)
Incident Power at Port 1* 0.01 (W) 0.01 (W)Reflected Power at Port 1* 0.00227 (W) 0.00102 (W)Consumed Power at Port
2* 0.00692 (W) 0.00132 (W)
Material Losses*=0.000817-8.3525e-11
= 0.000817 (W)=0.00765-1.48793e-7
=0.00765 (W)
Step 2 Press down “Shift” and window all the polygons on the window. Select Delete in Edit menu to delete all the polygons. We are going to re-build the polygons.
Step 3 Select Rectangle in Entity menu. MGRID will prompt you for the parameters of the rectangle. Enter the parameters as shown in Figure 5.15. Basically, we want to build a rectangle centered at (x, y, z) = (0, 0, 31) with length = 1512 mils and width = 1500 mils. Select OK.
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Figure 5.14 The illustration of a simple edge-fed patch antenna.
Table 5.7 The parameters of the patch antenna.Substrate Thickness 31 mils Dielectric Constant 4.4
Patch Length, L 1512 mils Patch Width, W 1500 milsInset Width, S 115 mils Inset Depth, D 452 milsStrip Width, T 60 mils Feed Line Length, F 750 mils
Figure 5.15 The parameters for the patch.
Response:The rectangle corresponding to the vertices 1, 2, 3 and 4 in Figure 5.14 is built.
Step 4 The next step is to build the inset. There are many ways to build it. We will just show the simplest way. Press down “Shift” button, window the two vertices on the right (or the vertices 1 and 2 in Figure 5.14) of the rectangle.
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The two vertices are selected.
Explanation:The formal way to select vertices is to select Select Vertices in Edit menu. Then,
window the vertices you like. Pressing down the “Shift” key is a fast way to get into the selection mode. If you window some polygon(s), MGRID will automatically get into the Select Polygon Group mode. If you window some vertices without any complete polygon, MGRID will automatically get into the Select Vertices mode in Edit menu.
Step 5 We are going to build the inset on the selected edge. Select the Cut into Polygon on Edge in Adv Edit menu.
Response:MGRID will prompt you for the dimensions of the cut.
Step 6 Please change the Cut Width to 115 mils and the Cut Depth to 452 mils. While you change the parameters, some related parameters are updated automatically. Basically, the users can enter the parameters in other ways. The user also change make the inset to be off-centered. For our example, we want it to be centered. Please select OK to continue.
Response:The inset will be created. The picture will be similar to Figure 5.14 except there is not
feed line. The rectangle becomes a polygon of 8 vertices.
Step 7 We are going to build the feed line. Press down “Shift” button. Window the vertices 5 and 6 (see Figure 5.14) of the 8-vertex polygon to select them. Select Continue Straight Path in Adv Edit menu. We are going to build the feed line on the edge formed by vertices 5 and 6.
Response:The Continue Straight Path dialog comes up (see Figure 5.16).
Step 8 Change the Path Length to 1202 mils (the D+F in Table 5.7). Change the Path Start Width to 60 mils. The Path End Width is automatically updated to 60 mils. Select OK to continue.
Response:The edge-fed rectangular patch antenna with inset is built.
Step 9 Select Port for Edge Group in Ports menu. Select the Extension for MMIC Circuit scheme. Select OK to accept the other default values. The Edge Group Focused Layers dialog comes up. We do not need to change the focus. Window the edge (or the two vertices) at the end of the feed line. The port 1 will be defined on the edge. Select Exit Port to exit the Port for Edge Group mode. We will get the structure ready for simulation (see Figure 5.17). Save the geometry file as: c:\ie3d\samples\rpatch2.geo.
Step 10 Select Simulate in Process menu. Enter Start Freq = 1.8 GHz, End Freq = 2.0 GHz, Number of Freq = 101. Select Enter to enter the frequency points into the list. Please enable Adaptive Intelli-Fit (AIF). Please disable Current Distribution File and Radiation Pattern File. Enable Automatic Edge Cells (AEC) with Edge Width = 10 mils. Select OK to simulate the structure. The simulation takes less than 10 seconds on modern PC. After the simulation, MODUA is invoked to display the results. If the displayed results are not in Cartesian coordinate system, please select Define Display Graph in Process menu of MODUA. Select dB and Phase of S-parameters and select OK. Select dB[S(1,1)] and select OK to get the s-parameters displayed on Cartesian coordinate (see Figure 5.18).
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Figure 5.16 The Continue Straight Path dialog for the path.
Figure 5.17 The completed patch antenna ready for simulation.
Section 11. Defining Optimization Variables for Tuning and Optimization.
As we can see, the above section demonstrates how we can model a typical antenna. The simple antenna is resonating at 1.86 GHz. The dB[S(1,1)] is slightly above –10 dB. In some sense, it is not a well-designed antenna. A well-designed antenna should have dB[S(1,1)] below –10 dB in some frequency band. One question you may have is whether we can tune some dimensions of the antenna to see how the dimensions affect the performance of the antenna. The more advanced question is whether the IE3D can optimize the dimensions for specified performance.
Tuning and full-wave electromagnetic optimization are both implemented in the IE3D. In the following sections, we will discuss how we tune the dimensions of an antenna, and how we optimize the dimensions of the antenna for specified performance. The 1st step for tuning or optimization is to define the optimization (or tuning) variables.
Assume we want to optimize the antenna for perfect match at 1.9 GHz. Our goal is to achieve dB[S(1,1)] = -∞ (or |S(1,1)| = 0) at 1.9 GHz. In fact, the goal should be better interpreted as: Re[S(1,1)] = 0 and Im[S(1,1)] = 0 or the locus of the frequency response goes through the origin of the Smith chart at 1.9 GHz. Mathematically, the solution for Re[S(1,1)] = 0 and Im[S(1,1)] = 0 is a single root. However, the solution for |S(1,1)| = 0 is a double root.
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Figure 5.18 The s-parameters of the patch antenna.
Experienced antenna designers will know that changing the patch length will change the resonant frequency of the antenna. Changing the inset depth will change the matching significantly and the resonant frequency slightly. For our tuning example, we will show how we can tune the length of the patch.
Step 1 While the rpatch2.geo is still opened, press down “Shift” and window the vertices 1, 2, 3 and 4 in Figure 5.19 to select them. You can select all the 4 vertices in one shot, or select them one by one. We are going to define them as the 1st optimization variable. Basically, we want to tune the x-coordinates of the vertices.
Figure 5.19 The illustration of the vertices in defining the optimization variables.
Step 2 Select Variable for Selected Objects in Optim menu. The Optimization Variable Definition dialog comes up. On the IE3D, we use vertices’ locations to change the shape of the circuit. The Optimization Variable Definition dialog shows the vertices locations. Totally, we have selected 4 vertices. All of them are distinct vertices. In case there are polygon connections, at a single location, there might be multiple vertices. We will see the Selected Vertices count is different from the Distinct Vertices count. This is the 1 st time we define a variable. We want to map the vertices to a new variable. For the selected vertices, we want to change their x-coordinates. Therefore, we want its Tuning Angle to be 0 (or 180) degrees. The Tuning Angle
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is the angle of the direction and the x-axis. We want this variable to be commented as: Patch Length. Therefore, please enter the Tuning Angle and Variable Comment as they are shown in Figure 5.20. Select OK to continue. The x-coordinates of the 4 vertices are defined as optimization variable. The status window indicates that it is in the Low Bound definition.
Figure 5.20 The Optimization Variable Definition dialog.
Step 3 Move the mouse somewhere to the left. You will see some lines are following the mouse. Click the left mouse button. MGRID shows the Set Low Bound dialog. Please change the Low Bound value to –150 mils. Select OK to continue. The status window will indicate that it is in the High Bound definition.
Step 4 Move the mouse somewhere to the right. You will see some lines are following the mouse. Click at the left mouse button. MGRID shows the Set High Bound dialog. Please change the High Bound value to 150 mils. Select OK to continue.
Response:The x-coordinates of the 4-vertices are defined as the 1st optimization variable.
Explanation:When we define the low and high bounds, we need to be very careful about the facts:
(1). Wide bounds (bigger difference between high bound and low bound) will allow more searching space for our optimizer. However, wide bounds will make the optimization more difficult to converge. If possible, we will suggest a user to tune the circuits closer enough to the goals before he starts an optimization. (2). When we define the bounds on the IE3D, we need to make sure the geometry is still valid in the range. For our example, our initial Patch Length is 1512 mils. We cannot define the low bound of the 1st variable to be smaller than or equal to –1512 mils. Otherwise, the geometry will not be valid even you can still define it.
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When the IE3D detects the geometry is not valid, it will stop the simulation or optimization. Avoiding invalid geometry for multiple optimization definitions is skillful. We will discuss such an example later.
Step 5 Save the geometry as: c:\ie3d\samples\rpatch3.geo.
Section 12. Electromagnetic Tuning Simulations.
We have defined an optimization variable to control the length of the patch. We may want to perform some tuning simulations on the patch length. We can setup the tuning simulations in one shot.
Step 1 Select Simulate in Process menu of MGRID. The 101 frequency points should be still in the list box. All the already setup data are unchanged: AEC enabled with edge width = 10 mils, AIF enabled, Current Distribution File and Radiation Pattern File disabled.
Step 2 In case, you stopped the MGRID for a break before Section 12, the last setup information will be lost. How can you guarantee you will have the same settings as some previous simulations? You can select the Retrieve button. Then, you select the rpatch2.sim file. The settings on the rpatch2.sim file will be recovered into the dialog.
Step 3 Select the Define button in the Tuning Setting portion of the Simulation Setup dialog (on the lower right corner). MGRID will prompt you for the Tuning Range for the No.1 Variable (Figure 5.21). Enter the Number = 7, Start = -150 and End = 150. Select OK. Basically, we want to simulate the structure with the No.1 variable = -150, -100, -50, 0, 50, 100 and 150. MGRID resumes to the Simulation Setup dialog. Please check the File Name Style on the lower right of the dialog. It should be Including Tuning Indices. Select OK.
Figure 5.21 The Tuning Range dialog for the No.1 variable.
Response:A batch file will be created. Each line of the batch file is a command to invoke the
IE3D simulator for an offset value of the No.1 optimization variable. There are total 7 commands to invoke the IE3D. The batch file will be run automatically. Each IE3D is invoked to simulate the case. After the simulation, a MODUA is invoked to display the result. Then, the next IE3D is invoked. It takes about 1-2 minutes to finish all the 7-simulations.
Explanation:After the 7-simulations are done, there will be 7 MODUA displaying the s-parameters
in 7 data files: rpatch3_0.sp, rpatch3_1.sp, rpatch3_2.sp, rpatch3_3.sp, rpatch3_4.sp, rpatch3_5.sp, and r_patch3_6.sp. The rpatch3_?.sp contains the s-parameters when the No.1 variable is: (-150 + ?*50) mils, where “?” takes the value of 0 to 6. The relationship between the files and the patch length is documented in Table 5.8.
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In case we had multiple optimization variables. the file name will be of the style of: rpatch3_2_1.sp.
Also, if the user choose the File Name Style as: Including Tune Quantities instead of Including Tune Indices, the offset values of the variables will be included in the file names. However, the file names may be very long.
Table 5.8 The relationship between files, variable value and patch length.Variable Value File Name Patch Length, L
Step 4 Please use the Parameter File Queue in File menu and the Display Queue Items in View menu of MODUA to display the results of 7-simulations onto one MODUA. We will not repeat the steps of putting multiple data into one graph. Interested users should read the sections 7 and 8 of Chapter 3.
Figure 5.22. The comparison of the results with different Patch Length.
Explanation:As you can see, the resonant frequency is at about 1.82 GHz when L = 1562 mils and
about 1.99 GHz when L = 1612 mils. By adjusting the variable, we will be able to find the L value with the resonant frequency exactly at 1.9 GHz. From the trend, you will not expect that the antenna to be perfectly matched at 1.9 GHz when you adjust the L. Experienced antenna designers will know that we should also adjust the inset depth D for the matching. It will take much time and effort if we try to use the tuning method to find the location of patch. We can use the built-in optimizer to do it for us.
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Section 13. Multiple Optimization Variables and Planning to Avoid Invalid Geometry.
Step 1 Save the file as c:\ie3d\samples\rpatch4.geo. Select Change Variables and Calls in Optim menu of MGRID. We are going to reduce the bounds because we really do not need to define so wide a bound for the optimization.
Response:The Change Variables and Calls dialog comes up. The only one variable is listed in the
listbox.
Step 2 Double-click at the No.1 variable in the listbox. The Change Variable Properties dialog comes up. Change the Low Bound = -70 and the High Bound = 20 (see Figure 5.23). Select OK to go back to Change Variables and Calls dialog. Select OK to finish changing the bounds.
Figure 5.23 The Change Variable Properties dialog.
Step 3 We are going to define the inset depth D as the 2nd optimization variable. Press down “Shift” button and window the vertices 5, 6, 7 and 8 in Figure 5.19 to select them. Select Variable for Selected Objects in Optim menu. The Optimization Variable Definition dialog comes up. It shows that 6 vertices are selected. You may think only 4 vertices are selected. What MGRID shows 6 vertices? In fact, vertices 6 and 7 in Figure 5.20 are common vertices for two polygons. We are going to define the insert depth D as a new variable. Select New Variable for the Vertices Mapped To combo. We are going to change the x-coordinates of the vertices. Therefore, we enter the Tuning Angle = 0. Enter the Variable Comment as: Insert Depth. Select OK to continue.
Response:The status window indicates that it is in defining Low Bound mode.
Step 4 Move the mouse to the left and click. Enter the Low Bound as –120 mils. Select OK.
Response:The status window indicates that it is in defining High Bound mode.
Step 5 Move the mouse to the right and click. Enter the High Bound as 30 mils. Select OK to finish the definition of the 2nd variable. Save the change into: c:\ie3d\practice\rpatch4.geo again.
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Explanation:A user may wonder why we define the Low Bound = -120 and High Bound = 30. They
are not symmetrical. The reality was that, when we prepare this manual, we did try to define Low Bound = -100 and High Bound = 100 and ran the optimization. We found the solution was in fact below the Low Bound. To simplicity, we will not document the complete procedure. We just define a wider Low Bound for it. In reality, we may need to optimize the structures multiple times with improved bounds.
What is saved in the c:\ie3d\practice\rpatch4.geo is a correct geometry. It should be ready for optimization. However, the meanings of the variables may not be as we expected. We define the No.1 variable as Patch Length and the No.2 variable as Inset Depth. They are not exact. For the No.1 variable, when its value is increasing, the Patch Length is increasing. However, the Inset Depth is also increasing too. We can write down the relationship between the Patch Length, the Inset Depth and the variable 1 (or v1) and variable 2 (v2):
Apparently, the Insert Depth is not only control by the v2, but also the v1. When a length is determined by one single variable, we just need to guarantee the Low
Bound and High Bound do not exceed some limits. When a length is determined by multiple variables, we need to be very careful about the Low Bounds and High Bounds of all the variables so that their combinations do not exceed the limits. For our two variables examples, to make sure the Inset Depth is larger than 0, we need to make sure the sum of the Low Bound of v1 and the High Bound of v2 will not below –452. In our example, we have guaranteed it. However, the real situation may be much more complicated. It would be nice that we can make each variable to control one dimension. Then, the bounds are much easier to decide.
For our example, when we define the No.1 variable, if we had selected the vertices 5, 6, 7 and 8, as well as vertices 1, 2, 3 and 4, the v1 would have changed the Patch Length only. It would not change the Inset Depth. We can re-define the variable 1. However, there is some other way to go around.
Section 14. Add Optimization Calls to Optimization Variables.
If we select vertices 5, 6, 7 and 8 again, and associate it with the variable 1 to make sure the vertices 5, 6, 7 and 8 move simultaneously with the vertices 1, 2, 3 and 4, the Inset Depth will be kept the same while the variable 1 is changing.
Step 1 Press down “Shift” button and window vertices 5, 6, 7 and 8 in Figure 5.19 to select them. Select Add Selected Objects to Variable in the Optim menu. The Optimization Variable Definition dialog comes up.
(3) Tuning Rate = 1. Accidentally, the default settings are what we want. If we accept the default settings here, it means that the vertices 5, 6, 7 and 8 will be moving at the angle of 0 degree (0 axis). Its changing rate is 1 so that it will move at the same speed as the No.1 variable (or vertices 1, 2, 3 and 4).
Step 2 Enter the Call Comment as: “unrelated inset depth with v1”. Select OK to continue. Save the geometry as: c:\ie3d\practice\rpatch5.geo.
Explanation:
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For the rpatch5.geo, when the v1 is changing, the vertices 1, 2, 3, 4, 5, 6, 7 and 8 are changing correspondingly. The Patch Length is changed. However, the Inset Depth will not change because we have associate the change of the vertices 5, 6, 7 and 8 with the change of the vertices 1, 2, 3 and 4. For the No.2 variable, only vertices 5, 6, 7 and 8 are changing with the v2. Therefore, we can write down:
Patch Length = 1512 + v1Inset Depth = 452 – v2
The optimization variables on both rpatch4.geo and rpatch5.geo are valid. However, the physical meaning of the variables in rpatch5.geo is clearer than in rpatch4.geo.
Section 15. Electromagnetic Optimization.
Both rpatch4.geo and rpatch5.geo are ready for optimization. They should yield the same results. Let’s take the rpatch5.geo as the example.
Step 1 While the rpatch5.geo is opened, select Optimize in Process menu. The Optimization Setup dialog comes up. It is very similar to the Simulation Setup dialog. In fact, they share the same dialog resource. If the 101 frequency points are still there, please select Delete All button to delete all the frequency points on the list. Then, enter 1.9 for the Start Freq and click at enter. The frequency of 1.9 GHz is added into the list. Please uncheck the AIF because we cannot use it for one single frequency point. The next step is to define the optimization goals.
Step 2 Select the Add button in the Optimization Definition group. The Optimization Goal dialog comes up (see Figure 5.24). Enter the Start Freq = 1.9 GHz, End Freq = 1.9 GHz. Select the Quantity as Re(S). Select the 1st Parameter as: (1, 1). Select the Operator as By Itself. The 2 nd
Parameter will be grayed out. Select the Objective Type as: Optimization Quantity = Objective1. Enter the Objective1 = 0. The Objective2 will be grayed out. Enter the Weight = 1, the default value (see Figure 5.24). Select Ok to add the goal into the Optimization Definition list.
Step 3 Select the Add button in the Optimization Definition group again. The Optimization Goal dialog comes up again. The goal we defined in Step 3 is used as the default. Certainly, we do not want to define the same goal again. Change the Quantity to Im(S). Make sure other parameters are not changed. Select OK to continue. The 2nd goals will be added into the list.
Step 4 Change the Optimization Scheme from the default Genetic Optimizer to Powell Optimizer. We will have the Optimization Setup dialog shown in Figure 5.25. The error function is automatically generated by IE3D. However, for this optimization, the error function should be quite monotonic. We do not need to use Genetic optimizer that is good for multiple local minima. The Powell optimizer should do a faster job for it.
Explanation:On IE3D 9.0, we are offering 3 robust optimization schemes: (1) Random, (2) Powell,
and (3) Genetic. The Powel optimizer is one of the best in local optimization. When the starting point is
close to the goal, the Powel optimizer can reach the goal very fast. However, local optimizers are not good when the error function, which determines how close the current state is to the goal, has multiple local minimums.
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Figure 5.24 The Optimization Goal dialog for the 1st goal.
Figure 5.25 The Optimization Definition dialog after the goals are defined.
The Random and Genetic optimizer are the so-called global optimization schemes. They are very robust and they are suitable to multiple optimization variables. However, their convergence is normally slower than the local optimizer when the current state is close to the goal. Combination of local optimizations and global optimizations are normally suggested for efficient and robust electromagnetic optimizer. Compared to the Random optimizer, the Genetic optimizer should be more intelligent. It should be a better choice for general-purpose electromagnetic optimization.
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Table 5.9 Different types of parameters users can define.Parameters Description
S-ParametersdB, Re, Im, Mag and Ang of S(i,j)
The users are allowed to optimize s-parameters when there are ports on the circuits.
Y- and Z-ParametersRe, Im, Mag and Ang
of Y(i,j) and Z(i,j)
The users are allowed to optimize the y- and z-parameters when there are ports and s-parameters extracted are not generalized s-parameters (normalized to ports). The Zc of each port can be re-defined and it is not necessarily to be 50-ohms. If a user wants to change the Zc to non-50 ohms, he can select the port or excitation in the Excitation and Termination combo and select Modify.
Radiation Pattern ParametersGain, Directivity, Efficiency for
both LP or CP, Axial Ratio, Pattern Shape,
In order for MGRID to list the pattern parameters in the parameter types, a user needs to check the Radiation Pattern File before he adds the optimization goals. When he enables the Radiation Pattern File, MGRID will first prompt the user to define the angles of pattern calculation, the excitation and termination.
Combination of the Above Parameters
You can define the goals as different parameters with different weights.
Table 5.10 Different types of goals users can define.Parameters Description
The user can define the simple goals for a parameter. The PAR can be any parameters in Table 5.9. A typical example is: dB[S(i1,j1)], Re[Z(i1,j1)], Gain LP (linear Polarization), etc.
Ratio GoalsPAR = objective1PAR < objective1PAR > objective1
objective1 < PAR < objective2
The user can define the ratio of two parameters as the goal, or the PAR can be the ratio of different parameters: |S(i1,j1)|/|S(i2,j2)|, Re[Z(i1,j1)|]/Im[Z(i2,j2)], etc.
Symbolic GoalsPAR = symbol + constantPAR < symbol + constantPAR > symbol + constant
The user can define a parameter, or a ratio of two parameters as a symbol. Then, he can define a parameter, a ratio of two parameters (PAR) with comparative formula as listed in the left.
In the steps 3 and 4, we have defined the goals of the optimization as: Re[S(1,1)] = 0 and Im[S(1,1)] = 0 at f = 1.9 GHz. The weight for the two goals is 1. The weight is a way to balance which goals are more important in a multiple goal definition. As you can see, there are a few parameters in the Optimization Goal dialog. Using the parameters, we can define the goals symbolically with simple formulas. Tables 5.9 and 5.10 show the different types of parameters and different types of goals you can define on the IE3D optimization.
On Figure 5.25, a user can see some Optimization Control Parameters on the left of the Add button: Iteration = 20, OutBound = 5, FunctionError = 0.01, LocationError = 0. It means that we will perform maximum 20 iterations in the Power optimizer. OutBound is the maximum outbound times. In fact, this parameter is no long used. When the error function goes below 0.01, it will be considered as the optimization is converged. The user does not have access to the error function. The error function = 0.01 may not give a quantitative idea to the user. It is possible a user may define some very serious requirements on the goal so that
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the error function will never goes below 0.01. For such a case, the LocationError is used as the criteria of convergence.
Genetic optimizer is even more useful than Powell optimizer especially in wide band optimization. If we optimize the bandwidth of an antenna or a filter, the error function normally may have many local minimums. A user is suggested to use Genetic Optimizer in such a case. For the Genetic Optimizer, the control parameters are: FunctionError , ZeroOffset=1, StdDev, Generation, PopulationSize, MutationRate, and CrossOverRate. Those parameters are automatically set by MGRID. The user can change them by select the Optimization Scheme again in the combo box. Then, MGRID will prompt you to change them. A user can increase the Generation for more simulations. The more simulations you run, the closer the optimized performance is to the specified goals. The PopulationSize, MutationRate, CrossOverRate may affect the convergence speed.
Step 5 Select OK in the Optimization Setup dialog. MGRID will invoke the IE3D to start the optimization. It will do the iteration automatically. It will finish the optimization in 1 to 3 minutes. The final window of the MGRID is shown in Figure 3.26.
Figure 5.26 The IE3D window after the optimization is done.
Explanation:The IE3D window shows that the Optimization Scheme is PowellOptim. There are 2
variables. It totally did 92 simulations. However, only 76 of them are with distinct values for the optimization variables. IE3D only does 76 simulations. The “565” means that the IE3D will do maximum 565 simulations only for the genetic optimizer. For the Powell optimizer, it does not have the meaning. There is a section called Residual: The 1 st value is the residual of the last simulation. The 2nd value is the minimum residual in all the past simulations. The last value is the criteria for convergence.
For the window in Figure 5.26, it is the state when the optimization is done. The Residual is 0.007554 and it is below the criteria. It is converged.
A user should know that he could terminate the optimization anytime during the optimization. As long as the optimizer has finished at least one simulation, the current best result will always be saved in the file: rpatch5m.geo (appending a character “m” at the end of the file). A user can open the rpatch5m.geo for further optimization or analysis.
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Step 6 Open the c:\ie3d\practice\rpatch5m.geo. MGRID will prompt you there are variables defined on the geometry and whether you want to remove the variables for further editing. Any further editing will remove the optimization variables defined. Select NO to continue.
Step 7 Select Simulate in Process menu. Enter total 101 frequency points from 1.8 to 2.0 GHz. Remember to enable AIF. The AIF was automatically un-checked due to the fact that it was un-checked in the optimization setup. Select OK to continue.
Figure 5.27 The frequency response of the optimized antenna (rpatch5m.geo).
Explanation:MGRID will invoke IE3D to simulate the structure. It will finish in a few seconds.
Then, MODUA is invoked to display the s-parameters. We can define Display Graph or Display Smith Chart. The displays are shown in Figure 5.27. As you can see, the locus passes the origin of the smith chart. The dB[S(1,1)] is below –40 dB at 1.9 GHz. We can consider it as perfect match at 1.9 GHz.
Section 16. Radiation Pattern Display.
We are going to simulate the structure again and find its radiation patterns at selected frequency points. The simulation we performed on rpatch5m.geo created the s-parameters only. It does not contain the current and pattern data. The current data and pattern data files are normally much bigger. We would like to suggest users to choose to save the current and pattern data at selected frequency points only.
Step 1 Save the file: rpatch5m.geo as rpatch5m1.geo. Select Simulate again. The Simulation Setup dialog comes up. Select Delete All in the frequency section to delete all the frequency points in the listbox. Enter Start Freq = 1.88, End Freq = 1.92, Number of Freq = 9. Hit enter key to define them into the listbox. Un-check AIF. Enable Radiation Pattern File. The Current Distribution File will be checked automatically. MGRID will also prompt you to change the angles, excitation and termination for the angle. For the single patch antenna with one port, we do not need to change much. Select OK to continue. Select OK to invoke the IE3D for the simulation.
Explanation:We can check Current Distribution File without checking the Radiation Pattern File. In
such a case, IE3D will save the current distribution. However, it will not do the pattern
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calculation automatically. We can perform the pattern calculation on MGRID opening the .CUR file in the post-processing. In our current case, we can let IE3D to do the pattern calculation automatically.
Response:Internally, the IE3D will simulate the structure first. After the simulation, it will do the
pattern calculation at each frequency point. After the pattern calculation, IE3D will invoke MODUA to display s-parameters, MGRID to display the simulated structure and current distribution, PATTERNVIEW to display the pattern results.
Step 2 Select the rpatch5m1.pat file in the list of PATTERNVIEW. Select the Pattern Properties in the Edit menu of PATTERNVIEW. We will have a list of the pattern parameters (documented in Table 5.11.
Table 5.11 The pattern parameters of the optimized antenna (rpatch5m1.geo) at selected frequency points.
Explanation:For every frequency point, we define 10 mW of incident wave from the 50-ohm
normalized incident wave voltage. However, the Input Power is less than that. The difference is the reflected wave from the antenna and it is absorbed by the source. Of the Input Power, only a fraction is radiated out. The difference is the loss due to the surface wave, metallic loss, and the dielectric loss. Radiation Efficiency is the ratio of the Radiated Power over Input Power. The Antenna Efficiency is the Radiation Efficiency minus the return loss at the port with respect to the 50-ohms. The Linear Directivity is determined by the shape of the pattern and it is almost frequency independent. Linear Gain is the Linear Directivity with the Return Loss deducted. Return Loss is the Incident Power minus the Input Power.
Step 3 Select OK to close the Pattern Properties window. While the pattern list window is activated, select 3D Pattern in Display menu. The 3D Pattern Selection dialog comes up. Select the 1.9 GHz. Select the Pattern Style as: Mapped 3D. Select the Scale Style as dBi(Directivity). You will get the dialog as shown in Figure 5.28. Select OK to continue. You will get the display of 3D mapped pattern (see Figure 5.30). Some users may not understand the meaning of 3D mapped pattern because similar display is not documented in most antenna books. We will discuss the meaning of the 3D mapped pattern later. We can rotate, zoom and pan the view in the same way as the 3D view on MGRID.
Step 4 While the 3D mapped pattern is the activated window, you will see the menu of PATTERNVIEW is changed. Select View Parameters in View menu. The 3D Pattern View Parameters dialog comes up. Change the Max(dB) from 6.21458 to 6. The color scale will be changed.
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Step 5 Select the pattern list window to activate it (the window with the rpatch5m1.pat file listed). The menu system will change back to the original one. Select 3D Pattern in Display again. Make sure the freq = 1.9 GHz is selected. Change the Pattern Style to True 3D. Change the Maximum dB to 6. Select OK to continue. The true 3D view will be shown with the same scale as the Mapped 3D View (see Figure 5.30).
Figure 5.28 The 3D Pattern Selection dialog.
Figure 5.29 The 2D Pattern display after the parameters entered in Step 6.
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Step 6 Select the pattern list window to activate it. Select 2D Pattern in Display menu. The 2D Pattern Display dialog comes up. Scroll to the rpatch5m1.pat: 1.9 GHz section. Check the E-total at Phi = 0 and E-total at Phi = 90. Select Elevation for Direction. Select 2D Pattern for Option. Select Cartesian Plot for Plot Style. Select dBi (Directivity) for Scale Style. Enter the Start = -18 and End = 8, Step = 3 dB. Select OK to continue. We will get the 2D Cartesian plot in Figure 5.30.
Step 7 Select the pattern list window to activate it. Select 2D Pattern in Display menu. The 2D Pattern Display dialog comes up. Scroll to the rpatch5m1.pat: 1.9 GHz section. You will see the E-total at Phi = 0 and E-total at Phi = 90 and still checked. Select Elevation for Direction. Select 2D Pattern for Option. Select Polar Plot for Plot Style. Select dBi (Directivity) for Scale Style. Enter the Start = -18 and End = 8, Step = 3 dB. Select OK to continue. We will get the 2D Polar plot in Figure 5.30.
Figure 5.30 The 4 different kinds of 2D and 3D patterns, and the coordinate systems.
Explanation:By comparing the 2D and 3D patterns, you will understand the difference of Mapped
3D and True 3D patterns. Basically, the 2D Cartesian plot is basically a cut of = constant on the Mapped 3D pattern. The 2D Polar plot is a cut of = constant on the True 3D pattern.
The horizontal axis of the 2D Cartesian plot and the cylindrical radius axis of the Mapped 3D pattern are for the elevation angle (). The vertical axis of the 2D Cartesian plot and the z-coordinate of the Mapped 3D pattern are for the magnitude of the pattern.
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The angle referenced to y-axis in the 2D Polar plot and the angle in the True 3D pattern are for the elevation angle (). The radius in the 2D Polar plot and the spherical radius in the True 3D pattern are for the magnitude of the pattern.
A user should be informed that the scaling in the Mapped 3D and True 3D patterns are changed in the IE3D 9.0. Before PatternView 9.0, the scaling is based upon |E| 2. The scaling in the PatternView 9.0 is based upon |E|.
For this particular example, there is an infinite ground plane. Therefore, the pattern is always -∞ at the angle of > 90 degrees. For the 2D Polar plot, we allow < 0. It corresponds to the > 0 with the ’ = ( 180o – ) case.
For layered structures with one or multiple substrates, the IE3D always predicts the pattern has a null at = 90 degrees. It is from the assumption of infinitely extended substrate. Actually, there exists the surface wave which decays as 1/√, where is the cylindrical radius when there is no dielectric loss, compared to the decay of 1/r, where r is the spherical radius, for the radiated field. Practically, there is always dielectric loss. The surface wave will decay exponentially. The surface wave power will be absorbed by the dielectrics.
For many symmetrical free space structures, we may be able to use the infinite ground plane to reduce the size of the problem to half of the original size. For example, we may use a monopole over an infinite ground plane to replace a dipole for the same results. In this case, remember to set the conductivity of the infinite ground plane to a very high value (>1.0e+15). Otherwise, you will see there is a null at = 90 degrees.
Step 8 Select the pattern list window to activate it. Select the Gain vs. Frequency Display in Display menu. The Frequency Response Display dialog comes up. We can choose the gain at any (, ) angles to display the gain at the angles compared to the isotropic case. Check the “Max” checkbox. We will display the curve for the maximum gain vs. frequency only. Make sure the Start Freq = 1.88 and End Freq = 1.92. Then, select OK to continue. The maximum gain is displayed in Figure 5.31.
Figure 5.31 The Gain Vs. Frequency plot.
Explanation:We can display many different parameters vs. frequency plots. We can also display the
azimuth pattern, the axial ratio pattern, etc. Not only that, we can use the Add Pattern in Edit menu to add more calculated pattern files (*.pat) into the list. We can compare the parameters
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of different patterns in one or multiple graphs. There are too many different plots available on the PatternView. We will not discuss each one.
Section 17. Adding Array Factors to Patterns.
To improve the directivity and gain of an antenna or change the pattern shapes, antenna designers put multiple antenna elements with appropriate spacing and excitation. Normally, there will be mutual coupling between the adjacent elements. We should simulate the elements simultaneously to get accurate modeling of the array. However, the simulation time will increase substantially. While the modeling of antenna array with mutual coupling included will be discussed in later chapters, we will discuss a simple way to predict the pattern of an antenna, the antenna array factor. When the spacing between elements is large enough, the mutual coupling between elements may be negligible. Though the mutual coupling is not negligible, we may still want to have a fast way to predict the pattern. In such a case, we can use the array factor approach.
Step 1 Select the pattern list window to activate it. Select Array Pattern Calculation in the Edit menu. The Antenna Array Parameters dialog comes up. Select the Add button. The Add Elements dialog comes up. For X-Location, enter the From = 0, To = 12400 mils. For the Y-Location, enter the From = 0, To = 12400 mils. Please note that 3100 is half a wavelength in air at 1.9 GHz. We are adding a 5 by 5 antenna array with spacing of half a wavelength. We will get the dialog shown in Figure 5.32. Select OK. The Antenna Array Parameters dialog is resumed. We will see total 25 elements are added into the list.
Figure 5.32 The Add Elements dialog after the data is entered in Step 1.
Explanation:We created a uniform 5 by 5 antenna array. In fact, we can define the Phase Step for the
added elements. In Figure 5.32, the Start Phase is for the 1st element. We can enter a set of array elements in the 3D space in each Add command. We can add more to them. For each Add command, we can designate which Element Index it is. For our current situation, we have only one type of element in the list: the rpatch5m1.pat. In case, we have multiple elements in the pattern list window, we can choose different elements for its Element Index (starting from 0). We can mix-use different types of elements for the antenna array.
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No only we can mix-use different types of elements for the array, for each Add command, we can also define the Rotation angles of all the elements to be added. For the Rotations, we need to enter the 1st Phi, 1st Theta and 2nd Phi. What do they mean? The angle or matrix transformations are like that: (1) We keep the z-axis unchanged and we rotate the angle for the 1st Phi; (2) Then, we keep the x-axis unchanged and we rotate the angle for the 1st Theta; (3) Finally, we keep the z-axis and we rotate the angle for the 2nd Phi.
Step 2 Select Export button and enter the file name as: rpatch5m1.arr. This step is not necessary. We are saving the elements into the array file so that we can import it for other arrays. When we try to find the array pattern with the same array factor, we can import the array factor back.
Step 3 Select Add Theta. The Add Elevation Angles dialog comes up. Enter Start = 0, End = 180, Number = 73. Select OK. The theta angles are added into the list. For more elements, we need to add more angles for smoother fitting in the pattern.
Step 4 Select Add Phi. The Add Azimuth Angles dialog comes up. Enter Star t = 0, End = 360, Number = 73. Select OK. The phi angles are added into the list.
Step 5 Check the Put Pattern into the Pattern List. We will get the picture shown in Figure 5.33. Select OK to continue.
Figure 5.33 The Antenna Array Parameters when all the parameters are entered by Step 5.
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Explanation:On the PatternView, it is allowed to include the effect of the Final Ground Plane (see
Figure 5.33). This is for the case we want to include the effects of the real ground plane. When we design an antenna, we always have a ground plane that is the reference of the patch. However, this ground plane may not be the final ground. For example, if we use an antenna on a base station. The final ground plane is the earth. If we want to know the effect of the earth, we can add it as the Final Ground Plane. In this example, we do not need it.
Response:The PatternView will start the calculation of the array pattern. After it finishes the
calculation, it will put the resulting array pattern file: rpatch5m1a.pat into the pattern list window.
Step 6 Select 3D Pattern in Display menu. Select the rpatch5m1a.pat file at 1.9 GHz. Select Mapped 3D for the Pattern Style. Select dBi (Directivity) for the Scale Style. Change the Max dB to 20. Change the Step dB to –4. Select OK to continue. A pencil-shaped array pattern is displayed. However, the white colors for the angles are distracting. Select the View Parameters in View menu. The 3D View Parameters dialog comes up. Change the Boundary from Yes to No. Select OK continue. We will get a more colorful picture (see Figure 5.34).
Figure 5.34 The comparison of the 3D pattern with and without boundary for the angles.
Section 18. Pattern Merging, Rotation and Wave Propagation Prediction.
There are a few more menu items in the Edit menu of PatternView. They allow users to rotation a pattern, add the final ground plane’s effect to the pattern, and merge multiple patterns. It also allows a user to predict the field propagation and distribution in the far field zone. The Wave Propagation prediction uses the far field pattern to predict the field density at a set of specified x, y and z-locations. Such a feature will be good for the wireless applications such as planning of base station locations. We will not show any more examples here. Interested users can try to explore the features on their own. We will conclude this chapter here.
