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

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

3. 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.

4. Start a new project and name it

5. Set the Defaults to suitable values and SAVE.

6. Open Layout and Change units

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

8. 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.

9. 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 )

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

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

12. Draw Rectangle (for feed line)

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

14. The patch and feed should look like this

15. Now change layer to “hole”

16. Draw a polyline at the edge of the feed line.

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

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

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

20. Ensure that port touches the line

21. Save the design

22. Start Momentum and Send all layout items.

23. The momentum window should look like this.

24. Setup Substrate

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

26. Map process layers: Map cond to first ------ line and set to Strip

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

28. Solve Substrate from 0.5 to 2 GHz.

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

30. 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.

31. Solved mesh looks like this

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

33. End of analysis is indicated in status window

34. S-Parameters

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

36. Radiation Patterns

37. 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.

38. Radiation pattern Status window indicates completion of radiation pattern computation.

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

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

41. Radiation Pattern Graph

42. Visualization

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

44. 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.

45. Save Work