Tutorial : Using “vias” to feed patch antennas Nilesh Kamdar Cynthia Furse Utah State University

This tutorial assumes you know: How to start Libra at USU Basics of Libra (see other Tutorials) Basics of using Layout and Momentum

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.

Start a new project and name it

Set the Defaults to suitable values and SAVE.

Open Layout and Change units

Draw a rectangle. (This the patch which needs to be via-fed)

Let size be 2 x 2 cm. (20000 x 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.

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 )

The feed line to be added cannot be on the same layer as the patch. It has to be a different layer.

Change Layer to cond2 (Draw>Entry Later...>cond2>OK)

Draw Rectangle (for feed line)

Bring it approximately close to the center of the patch and set width as 2 cms

The patch and feed should look like this

Now change layer to “hole”

Draw a polyline at the edge of the feed line.

Left-click to start drawing line and double-click to stop. (ESC to stop drawing)

The Layout should look like this: RedBlueYellow Note : Change layer back to ‘cond’ to do other additions to design.

Add Port to the other edge of feed line (detailed instruction in patch antenna tutorial)

Ensure that port touches the line

Save the design

Start Momentum and Send all layout items.

The momentum window should look like this.

Setup Substrate

Change substrate values to add 2 substrates, patch and feed. Both with Er = 2.2 and thickness 1588 microns Add Layers

Map process layers: Map cond to first line and set to Strip

Map cond2 to second line and set to strip. Map hole to “patch” substrate and set to Via.

Solve Substrate from 0.5 to 2 GHz.

Check status window to see if substrate analysis is complete (Note : Never close any such status window in Libra. They are very helpful)

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.

Solved mesh looks like this

Analyze Set analysis control to sweep from 0.5 to 2 GHz in steps of 0.25 GHz

End of analysis is indicated in status window

S-Parameters

Edit Measurements Edit>Measurements>More>(choose S11 and dB)>Add>Apply

Radiation Patterns

Radiation Pattern control Choose 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.

Radiation pattern Status window indicates completion of radiation pattern computation.

Choose different type of Graph Graph>New…>Far-Field-Planar>OK

Edit Measurements Edit>Measurements>More>(choose via1_rp\Fields)>(choose Etheta, Ephi, Etotal)>Add>Apply

Radiation Pattern Graph

Visualization

Visualization Control Choose plot type : current magnitude Choose frequency as 1 GHz Choose Color : Rainbow Choose Animation Speed : 15 Apply

Visualization Control After 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.

Save Work