The Point of a Parabola: Focusing Signals for a Better Wireless Network

Building Your Parabolic Reflector

1. Download the parabolic reflector template, shown in Figure 4, below.
2. Print the template on an 8.5 x 11 inch sheet of paper.
3. Use a ruler to check that the sides of the calibration square in the corner of the sheet are of equal length. If the square appears skewed (one side is longer than the other), you will need to adjust the settings on your printer (for example, the page margins) and try again.

Figure 4. The parabolic reflector template.

4. Use scissors to cut out the outline of one of the parabolas, as shown in Figure 5, below. A second parabola is provided in the template in case you make a mistake with the first one.

Figure 5. Use scissors to cut out the parabola.

5. Trace two copies of the parabola onto a piece of corrugated cardboard, as shown in Figure 6, below. Make sure you poke a hole in the cardboard for the focal point.

Figure 6. Trace the parabola onto corrugated cardboard, using the tip of the pen to poke a hole in the cardboard for the focal point.

6. Use scissors to carefully cut the parabolic shapes out of the corrugated cardboard, as shown in Figure 7, below.

Figure 7. Use scissors to cut the parabolas out of the cardboard.

7. Use a pen or pencil to make a small "+" symbol (about 1 centimeter [cm] wide) centered on each focal point. Then, use a sharp knife to cut slits in the "+", as shown in Figure 8, below. This will make it easier to push your Wi-Fi router's antenna through the cardboard when you do your testing.

Figure 8. Cut slits at the focal point so you can push the antenna through the cardboard.

8. Use scissors to cut four small rectangles and four small triangles out of your scrap pieces of corrugated cardboard. The exact size of these pieces is not critical — they will be used as spacers to separate your two parabolas. Use Figure 9, below, to get a rough idea of the appropriate size.

Figure 9. Cut out small cardboard spacers in the shape of triangles and rectangles.

9. Glue the two cardboard parabola pieces together, using the spacers as shown in Figure 10, below.

Figure 10. Glue the two cardboard parabolas together, using the small spacers.

10. Use scissors to cut out one side of a cereal box. Make sure the side is at least 20 x 25 cm (the Cheerios® box in Figure 11, below, is slightly larger, 29 x 24 cm). Cover one side of the cardboard completely in aluminum foil, and tape the edges of the aluminum foil to the back side of the cardboard cereal box, as shown in Figure 11.

Figure 11. Cover a thin sheet of cardboard in aluminum foil.

11. Attach the aluminum foil-covered cardboard to your parabolic template, as shown in Figure 12, below.
    1. Use a sharp knife to punch small holes near the edges in opposite sides of the foil-covered cardboard (centered on the height of the cardboard, as shown in Figure 12), so you can thread a string through them.
    2. Have a volunteer hold the cardboard in place against the curved edge of the parabolic template, while you thread the string from hole to hole in the cardboard and tie it tightly in place so the cardboard holds its curved shape. Make sure you pull the string taut before tying it tightly in place, otherwise the cardboard will not properly hold its shape.
    3. Use tape to secure the foil-covered cardboard to the parabolic template. This will enable you to mount the entire structure on your router's antenna.

Figure 12. Use string and tape to secure the foil-covered cardboard against the curved edge of the parabolic template. Top left: Even though the foil-covered cardboard has not been taped to the parabolic template yet, the string helps the cardboard hold its curved shape. Top right: Duct tape holds the foil-covered cardboard to the parabolic template, which will mount to the router's antenna. Bottom left: a close-up shot of string tied to a hole near the edge of the foil-covered cardboard. Bottom right: A side view showing the two locations where the string attaches to the foil-covered cardboard.

12. Your completed parabolic reflector should be able to stand up on its own, as in Figure 13, below. If your reflector seems flimsy, try using additional tape or cardboard to strengthen it if necessary.

Figure 13. A completed parabolic reflector.

Setting Up Your Wireless Router

1. Check to see which type of antenna your router has. Some wireless routers, like the one in Figure 14, below, have two external antennas. Others may have only one external antenna, or they may have internal antennas. If you cannot see an antenna on the back or sides of your router, that means it has an internal antenna.
   1. If your router has an internal antenna, you will need to purchase a USB Wi-Fi antenna for use with a laptop or desktop computer (see the Materials list), and adapt the rest of the Procedure to attach the parabolic reflector to this antenna, instead of the router's antenna.

Figure 14. A wireless router with two antennas.

2. If your router has two antennas, unscrew one of them from the back of the router, as shown in Figure 15, below. You will have to decide which antenna will be best for mounting your parabolic reflector (in this case, the antenna towards the top of the router), and then remove the other antenna (in this case, the one at the bottom). Keep the antenna in a safe place so you do not lose it, and remember to reattach it at the end of your experiment. Ask an adult if you need help.

Figure 15. Unscrew the second antenna, if there is one, from the back of the router.

3. Carefully slide your router's antenna through the focal-point slots on your parabolic reflector, as shown in Figure 16, below. Be careful not to break your reflector — if it is too hard to push the antenna through, use a knife to make the slots slightly bigger.

Figure 16. A completed parabolic reflector attached to the antenna of a Wi-Fi router. Note that the normal power and Internet cables have been disconnected from the router for this picture.

Build an Angle Template

1. Use a protractor, marker, and posterboard or large piece of cardboard to make an angle template like the one shown in Figure 17, below. Make sure that the template is large enough that you can still read the degree markings when the router and parabolic reflector are placed on top of it. It should have angle markings every 15°. Ask an adult for help if you have not used a protractor before.
   1. Note that +180° is the same as -180°. You can just mark it as +⁄-180° on your template.

Figure 17. Angle template ranging from 0° to +/- 180° in 15° increments.

2. You will use this template to adjust the angle of your parabolic reflector. Place the router in the middle of the template so that when you look straight down from above the router, the antenna lines up exactly in the middle of the template, where all the lines intersect. From here, you can adjust the aim of the parabolic reflector to the left or the right. It may help your aim if you draw an arrow in the middle of the cardboard part of the parabolic reflector (from the focal point to the edge of the cardboard), as shown in Figure 18, below.

Figure 18. From left to right, parabolic reflector oriented at -45°, 0°, and +45°.

Testing your Parabolic Reflector

1. Download and install a program for your wireless device (like a smartphone, tablet, or laptop) that can measure the signal strength of a wireless network. See the Materials section for suggestions.
2. Take some time to familiarize yourself with the program. Read online documentation or help-files, or ask an adult for assistance.
   1. Some programs will show information about every available wireless network nearby — remember that you only want to measure the signal strength of your wireless router. Be sure you know the name of your wireless network so you can find it in the program's list.
   2. Make sure you know how to measure the wireless signal strength in dBm. As explained in the Introduction, the dBm readings should be negative numbers. Some programs may provide other scales — for example "signal quality" on a scale of 0–100 — but you should use dBm if possible. If dBm is not an option at all, then it is OK to use "signal quality" instead. You may need to read your program's documentation or help files, or ask an adult to help figure this out.
   3. Once you have located your wireless network and learned how to measure its signal strength in dBm, experiment with the program by walking around your house with your wireless device. Does the signal strength change? This will help you learn how to use the program and take readings before you do your experiment.
3. Create a data table like Table 1, below, in your lab notebook. You will use this table to record your results. Your entries for the "control" rows may vary depending on the type of router you have. For example, if you have a router with two antennas, you can test it with only one antenna, and again with two antennas (in both cases without the parabolic reflector). If you purchased a USB Wi-Fi antenna for a laptop, you could measure the signal strength with the antenna (but no reflector), and the signal strength without the antenna, using the laptop's built-in wireless card.

4. Make sure the angle template you made is placed under your router, with the antenna centered in the middle of the template. Aim the parabolic reflector backward, at 180° (you may need to rotate the router itself slightly in order to do this — make sure the antenna stays centered).
5. Stand roughly 5 meters (m) in front of your wireless router, along the 0° line of your angle template. Now, there are several additional variables you must be careful to keep constant for the course of your experiment:
   1. Distance from the router: It is OK if you do not stand exactly 5 m from the router. Ideally, you should be in the same room as the router without any walls in between, but it is OK if you have to go into a separate room, or be slightly farther away or closer to the router, based on the layout of your house. The important thing is to keep the distance and location you stand in constant for the entire experiment.
   2. Height of the wireless device: Hold the wireless device at the same height as your parabolic reflector. For example, if your router is sitting on a desk, you may need to hold the wireless device at about waist or chest level. If the router is on the floor, you may need to squat down and hold your wireless device closer to the floor.
   3. Orientation of the wireless device: Make sure you hold the wireless device in the same orientation for each trial. For example, if you are using a smartphone, do not switch between holding it horizontally and vertically. Pick one orientation and use it for the entire experiment.
6. Use your Wi-Fi signal strength measurement program to take three readings of the signal strength in dBm. Record these readings for 180° in the table in you created in your lab notebook (note that -180° is the same as +180°, so you can enter the reading in both rows of the table).
7. Adjust the angle of the parabolic reflector to the next row in your data table (-165°). If you have a volunteer to help, she or he can adjust the antenna while you continue to stand in the same place with your wireless device. Otherwise, adjust the parabolic reflector yourself, then return to the exact same place you were standing.
8. Take three new readings and enter them in your data table. Note that -165° is not the same as +165° (that is only true for +⁄- 180°), so you should not duplicate the entry in your data table.
9. Repeat steps 7 and 8 for each remaining angle in your data table.
10. Remove the parabolic reflector from your wireless router's antenna. Take three final readings with your wireless device. These measurements are your control — they show you the baseline signal strength, without the use of a parabolic reflector. Comparing the readings with the parabolic reflector to the control will tell you whether the reflector made the signal strength better or worse. Remember to enter the three values in your data table.
    1. If your router originally had two antennas and you removed one, re-attach the second antenna. Take another set of three readings and enter them in a separate row in your data table. You can treat this as another set of control readings, or how your router performs in its "normal" state.
11. For each row in your data table, calculate an average of the three values and enter it in the final column.
12. Create a line graph with reflector angle (in degrees) on the x-axis and average signal strength (in dBm) on the y-axis. Also draw a horizontal line on the graph to represent the baseline signal strength with no reflector (you may need two lines if you took control readings with one and two antennas).
13. Analyze your results.
    1. What are the effects of the parabolic reflector?
    2. How does signal strength vary with angle of the reflector?
    3. How does the signal strength with the reflector compare to the baseline signal strength at different angles? Are there some angles where the reflector improves the signal strength, and others where the reflector makes the signal weaker?
    4. Based on your results, in what situations do you think adding a parabolic reflector to an antenna would make sense? When would using a parabolic reflector be a bad idea?
14. Remove the parabolic reflector from your router (or ask an adult if it is OK to continue using it). If you removed an antenna from your router, be sure to re-attach it.