Momentum for ADS 2001
LAB 3: Designing with Momentum
Via Fed Patch Antenna
This lab exercise shows how to draw a patch antenna with a via, setup
multiple substrate layers, and simulate the antenna response. Afterward,
the far field pattern can be viewed.
OBJECTIVES
?
Draw exact structure in the Layout window
?
Create multi-layer substrate definitions
?
Define and draw Vias
?
Mesh individual drawing layers
?
Reuse simulation files
?
Plot the impedance of the structure
?
Plot Far Field Radiation Patterns
3-1
Lab 3 – Using Momentum RF
RFIC Launch
TABLE OF CONTENTS
1.
Draw the Patch geometry with Coordinate Entry ...........3
2.
Draw the microstrip feed to the patch...................4
3.
Add a Port to the feedline .............................4
4.
Define the Port type as Single .........................5
5.
Draw the Via ...........................................5
6.
Set up the Substrate definition .........................6
7.
Map the Strip Metallization layers to the substrate .....7
8.
Map the Via to the substrate............................8
9.
Precompute the substrate ...............................8
10. Mesh separate Layers ...................................9
11. Set up the Simulation and solve .......................11
12. Plot the Simulation results ...........................12
13. Simulate again re-using simulation data ................14
14. Plot the Far Field Visualization.......................14
15. OPTIONAL STEPS........................................17
3-2
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
Procedure: Via Fed Patch Antenna
This patch design is fed with a microstrip and via from below the patch.
The results are close to the design goal. This lab will cover the details of
this via fed patch. You will create the antenna from scratch – no supplied
files are required.
Top view of the patch
antenna mesh.
Antenna Resonance at
about 3.8 GHz
1. Draw the Patch geometry with Coordinate Entry
a. Open a new layout window from the ADS Main Window and
save it with the design name: patch.
b. Be sure the entry layer is cond (default). Then click: Insert >
Coordinate Entry and the dialog will appear.
c. Click on the rectangle icon to start drawing the patch.
d. Enter the coordinates of the two diagonal corners in the dialog:
x= 100, y= 125 and click Apply. Then x= 600, y= -125 and click Apply.
3-3
Lab 3 – Using Momentum RF
RFIC Launch
NOTE: You can select Options / Layers. Change the shade display for the
cond layer from filled to outline. This will outline the geometry instead of
filling it.
2. Draw the microstrip feed to the patch
a. Make sure that Coordinate Entry is still active before starting
the next geometry. Change the drawing layer to cond2. This
will be the layer that is used for the feedline.
b. Select the rectangle icon to draw a Rectangle using coordinate
entry. Then enter the coordinates of the two diagonal corners:
x= 0, y= 5 and x= 320, y= -5 as shown here.
Entry layer
changed
to cond2.
3. Add a Port to the feedline.
a. As shown here, verify that the process layer is still on cond2 (1),
because the port must connect to the feedline rectangle on
cond2.
b. Select the Toggle Midpoint Snap Mode icon (2) to snap to the
center of the edge of the rectangle. Also, enable the Toggle
Vertex Snap Mode by clicking the icon (next icon to the left).
The vertex snap mode will be used for adding the via in a later
step.
c. Select the Port icon (3) and add the port to feedline left end (4).
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
4. Define the Port type as Single
a. Click on Momentum > Port Editor.
b. Select the port on the drawing and set it
to Single and click Apply. The
construction line reference plane will be
immediately drawn.
c. Exit the Port Editor: click OK.
5. Draw the Via
a. Set the entry drawing layer to hole (1). In general, there is no
significance to the process layer you choose except for certain
reserved process layers that are used by Momentum
2
Click and then
double click to
finish the polyline.
3
1
(construction line).
b. Verify that Vertex Snap mode is enabled.
c. Select the Polyline icon (2).
d. Zoom in very close to the end of the feedline. Then add the
polyline to the right end of the feedline (3): make sure to snap
to the vertex at each corner of the rectangle. When using the
polyline command, the mouse must be double-clicked left to
complete the drawing.
3-5
Lab 3 – Using Momentum RF
RFIC Launch
6. Set up the Substrate definition
a. In the Layout window, click: Momentum > Substrate >
Create/Modify.
Be sure Momentum is
selected and Not Momentum RF
b. Create a third dielectric layer named Alumina_2. Then click
the Add button. The new layer should be added below the
existing Alumina layer.
c. Set the thickness to 12.5 mil and the permittivity to 10.
d. Select the first dielectric Alumina, and set its thickness to 12.5
mils and permittivity to 10 also.
NOTE: DO NOT EXIT THIS DIALOG WINDOW YET.
3-6
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
7. Map the Strip Metallization layers to the substrate
a. In the Substrate editor, select the Metallization Layers tab.
b. Be sure that cond is mapped to Alumina as a Strip (shown here)
- this is the default in Momentum. Next, you will map the cond2.
c. Select the Layout Layer: cond2.
d. Click on the dashed line ( ------ ) between the Alumina and
Alumina_2 substrates. The dashed line is the interface between
the layers where Strips and Slots are mapped (not Vias).
e. Click on the Strip button to map cond2 as a Strip between the
two substrate layers as shown here.
3-7
Lab 3 – Using Momentum RF
RFIC Launch
8. Map the Via through the substrate
a. Select the Layout Layer: hole.
b. Click the Alumina dielectric (shown here). Vias are mapped to
dielectrics and not between interfaces.
c. Click the Via button. The result of the mapping is shown here:
hole is a Via which passes through the Alumina substrate layer.
d. Exit the dialog – click OK.
9. Precompute the substrate
a. Click Momentum > Substrate > Precompute.
b. Set the frequency from 1 to 10 GHz, and click OK.
c. OPTIONAL – Save the substrate to the database with a name
using the Save As command. Name it: patch_lay.
d. The computation will immediately run. Wait until it is finished
to complete the next step.
3-8
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
10. Mesh separate Layers
The feedline (cond2), like all transmission lines, can use Edge Mesh for
greater accuracy. The patch (cond) may not have high currents along its
edges, therefore Edge Mesh is unnecessary. Also, the patch can use a
coarser mesh to save simulation time. Vias are not meshed (they are
always one cell).
a. Begin by clicking
Momentum > Mesh > Setup.
Use the Global tab to set
the frequency value of 10
GHz for the layer meshes
that will be set up next.
Also, turn off Edge Mesh
as shown here.
Mesh Freq = 10
GHz
Cells per
? ?? ????
b. Select the Layers tab and
select the cond layer
(patch). Set it as shown
here: 15 cells/wavelength
and Edge Mesh OFF.
Cond: 15 cells ?
??No Edge Mesh
Edge Mesh: OFF
Cond2: 30 cells ? ?
Edge Mesh is ON
c. Select cond2 (feedline) and set 30 cells/wavelength - Edge Mesh
ON.
3-9
Lab 3 – Using Momentum RF
RFIC Launch
d. Click Momentum > Mesh > Precompute. The mesh will be
calculated but only if the substrate calculation has finished.
3-10
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
e. Verify that the mesh is complete and looks like the one shown
here.
11. Set up the Simulation and solve
a. Click: Momentum > Simulation > S-parameters.
b. Set up the following simulation: Sweep Type = Adaptive, Start
= 1 GHz, Stop = 10 GHz, and Sample Points Limit = 15 as
shown here. Use the Update button.
NOTE: DO NOT set the Solution Files (Reuse files) and Data Display (Open
data display) - they should remain unchecked as shown.
3-11
Lab 3 – Using Momentum RF
RFIC Launch
c. Run the simulation by selecting Simulate. This will take a few
moments. Afterward, the results will be written to the dataset
name shown: patch.ds which is the default name (same as the
design).
12. Plot the Simulation results
a. From the layout, open a new Data Display window: Window >
New Data Display. Then select patch_a as the default dataset.
b. Insert a rectangular plot and add S(1,1) in dB. With Adaptive
sweeps, a large number of data points are derived from a few
simulated data points. Here, approximately 15 frequencies are
analyzed and from those data points about 437 frequencies are
derived and stored in the dataset with the extension: _a.
This is the
derived value
from the AFS
simulation.
c. Insert a marker on the dB(S(1,1)) trace to determine the
resonant frequency.
OPTIONAL: If you add another
plot of two traces: real part of
Z0(1) for patch_a and real part of
Z0(1) for the patch dataset, you
can see the impedance looking
into the feedline.
Use Trace Options and put a
Symbol at data (circle) on the
patch trace to see the frequencies
where Momentum actually
performed an analysis . There are
several circles concentrated
around the resonance. This Z
3-12
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
value is calculated using the cross section and the dielectric. It should
match the driving circuit impedance, typically 50 ohms but does not..
3-13
Lab 3 – Using Momentum RF
RFIC Launch
13. Simulate again re-using simulation data
You can re-run the simulation to extend the frequency range or to simulate
at a specific frequency. To do this, add to the current list and reuse the
existing simulation data. For a far field radiation pattern, the results can
only be viewed for specific frequencies that have been solved. In the case of
this patch antenna, it is resonant in a very narrow frequency band. While
AFS (adaptive) can show the resonance, it may not actually simulate the
specific frequency of interest. Therefore, the reuse feature can be used.
a. Select the Sweep Type as Single.
b. Enter the frequency at the
resonance: 3.865 GHz and click the
Add to Frequency Plan List button.
c. Select Reuse files from previous
simulation button.
d. Simulate and answer Yes to the
question box that warns against
reusing data if you make changes
to the structure or the mesh. Note
that your plot will be updated.
3-14
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
14. Plot the Far Field Visualization
To examine the Far Field Plots, the resonant frequency must be selected
and the calculations performed.
a. Click: Momentum > Post-Processing > Radiation Pattern.
b. When the radiation Pattern dialog box opens, select the
frequency of 3.865 GHz which will appear in a list.
c. Check the following: 3D Visualization and Open display as
shown.
d. The Port 1 Excitation default settings should be: 50 ohms and
1V as shown here.
e. Click Apply and then click on Compute to start the calculation
of the far fields. The status will show a message and a new
window will open.
3-15
Lab 3 – Using Momentum RF
RFIC Launch
f. When the Visualization window opens, click: Far Field >
FarField Plot to open the Far Field Dialog box.
g. The following defaults should be in the dialog box as shown
here: View_1, E for the E field, Normalize and Log Scale with
the Minimum dB set to –40 as shown.
3-16
Chapter 3 – Using Momentum RF
Lab: RFIC Launch
h. Then click OK to display the plot.
i. When the Momentum Visualization window opens, you will see
a 3D-plot of your antenna.
15. OPTIONAL STEPS
Try these only if you have time.
1. Modify the feedline length and width to see the effects on the Sparameter results. Also, try making the feedline exactly 50 ohms along
the length (difficult to achieve).
2. Use multiple patches to achieve a desired radiation pattern.
3. Move the feedpoint on the patch to see the effects.
NOTE: After completing the optimization module, return to this lab exercise
and try to optimize the antenna to radiate at exactly 3.8 GHz.
3-17
Lab 3 – Using Momentum RF
RFIC Launch
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