Tutorial : Using vias to feed patch antennas

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Tutorial Using vias to feed patch antennas

• Nilesh Kamdar
• Cynthia Furse
• Utah State University

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This tutorial assumes you know

• How to start Libra at USU
• Basics of Libra (see other Tutorials)
• Basics of using Layout and Momentum

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Vias are used to feed patch antennas. They are
basically holes drilled through the substrate.
Generally a coax connector is fitted into the
hole, with a coax cable connected to the
connector.
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Start a new project and name it
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Set the Defaults to suitable values and SAVE.
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Open Layout and Change units
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Draw a rectangle. (This the patch which needs to
be via-fed)
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Let size be 2 x 2 cm. (20000 x 20000 microns)
For detailed instruction on rectangle drawing,
see patch antenna tutorial.
Note To get the grid of the Layout to the size
so that it can draw a 2x2 cm square, ZOOM OUT a
few times on the Layout Window.
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Draw a feed line to the point where the patch is
to be fed.(Let the feed be approximately the
center of the patch). In the tutorial use a 0.2
cm wide line as the feed. (For actual designs,
this line is generally a 50 ohm line. So use
LineCalc get the width of line at the required
frequency )
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The feed line to be added cannot be on the same
layer as the patch. It has to be a different
layer.
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Change Layer to cond2(DrawgtEntry
Later...gtcond2gtOK)
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Draw Rectangle (for feed line)
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Bring it approximately close to the center of the
patch and set width as 2 cms
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The patch and feed should look like this
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Now change layer to hole
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Draw a polyline at the edge of the feed line.
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Left-click to start drawing line and double-click
to stop. (ESC to stop drawing)
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The Layout should look like this
Red Blue Yellow
Note Change layer back to cond to do other
additions to design.
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Add Port to the other edge of feed line (detailed
instruction in patch antenna tutorial)
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Ensure that port touches the line
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Save the design
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Start Momentum and Send all layout items.
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The momentum window should look like this.
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Setup Substrate
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Change substrate values to add 2 substrates,
patch and feed. Both with Er 2.2 and thickness
1588 microns
Add Layers
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Map process layers Map cond to first ------ line
and set to Strip
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Map cond2 to second ----- line and set to strip.
Map hole to patch substrate and set to Via.
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Solve Substrate from 0.5 to 2 GHz.
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Check status window to see if substrate analysis
is complete(Note Never close any such status
window in Libra. They are very helpful)
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Next solve mesh and then analyze. (discussed in
patch antenna tutorial)Many such vias could be
added on a single patch. Most commonly a ground
point and a feed point are added. So two such
feed lines have to be added and one has to
connected to port (feed), while other is
connected to ground.
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Solved mesh looks like this
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AnalyzeSet analysis control to sweep from 0.5 to
2 GHz in steps of 0.25 GHz
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End of analysis is indicated in status window
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S-Parameters
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Edit MeasurementsEditgtMeasurementsgtMoregt(choose
S11 and dB)gtAddgtApply
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Radiation Patterns
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Radiation Pattern controlChoose a frequency (1
GHz). Also can set amplitude and phase of
excitation. Also if more ports are present one
can choose which port gets what
simulation.Planar is Elevation and conical is
Azimuthal.
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Radiation patternStatus window indicates
completion of radiation pattern computation.
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Choose different type of GraphGraphgtNewgtFar-Fiel
d-PlanargtOK
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Edit MeasurementsEditgtMeasurementsgtMoregt(choose
via1_rp\Fields)gt(choose Etheta, Ephi,
Etotal)gtAddgtApply
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Radiation Pattern Graph
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Visualization
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Visualization ControlChoose plot type current
magnitudeChoose frequency as 1 GHzChoose Color
RainbowChoose Animation Speed 15Apply
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Visualization ControlAfter visualization window
opens, Click Animate button in control
window.Try different plots like surface charge
etc.Also try different frequencies.Also try
different layers. One can see the feed line as
well as the patch being animated.
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Save Work
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Save Work