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# Cantenna

This antenna, sometimes called a Cantenna, uses a tin can as a waveguide and a short wire soldered on an N connector as a probe for coaxial-cable-to waveguide transition. It can be easily built at just the price of the connector, recycling a food, juice, or other tin can. It is a directional antenna, useful for short to medium distance point-to-point links. It may be also used as a feeder for a parabolic dish or grid.

Not all cans are good for building an antenna because there are dimensional constraints:

L

 Figure 4.32: Dimensional constraints on the cantenna.
1. The acceptable values for the diameter D of the feed are between 0.60 and 0.75 wavelength in air at the design frequency. At 2.44 GHz the wavelength λ is 12.2 cm, so the can diameter should be in the range of 7.3-9.2 cm.

2. The length L of the can preferably should be at least 0.75 λG , where λG is the guide wavelength and is given by:

For D=7.3 cm, we need a can of at least 56.4 cm, while for D=9.2 cm we need a can of at least 14.8 cm. Generally the smaller the diameter, the longer the can should be. For our example, we will use oil cans that have a diameter of 8.3 cm and a height of about 21 cm.

3. The probe for coaxial cable to waveguide transition should be positioned at a distance S from the bottom of the can, given by:

S = 0.25 λG

Its length should be 0.25 λ, which at 2.44 GHz corresponds to 3.05 cm.

The gain for this antenna will be in the order of 10 to 14 dBi, with a beam-width of around 60 degrees.

 Figure 4.33: The finished cantenna.

Parts list

• one screw-on N-type female connector
• 4 cm of copper or brass wire of 2 mm of diameter
• an oil can of 8.3 cm of diameter and 21 cm of height
 Figure 4.34: Parts needed for the can antenna.

Tools required

• Can opener
• Ruler
• Pliers
• File
• Soldering iron
• Solder
• Drill with a set of bits for metal (with a 1.5 cm diameter bit)
• Vice or clamp
• Spanner or monkey wrench
• Hammer
• Punch

### Construction

1. With the can opener, remove carefully the upper part of the can.

 Figure 4.35: Be careful of sharp edges when opening the can.

The circular disk has a very sharp edge. Be careful in handling it! Empty the can and wash it with soap. If the can contained pineapple, cookies, or some other tasty treat, have a friend serve the food.

2. With the ruler, measure 6.2 cm from the bottom of the can and draw a point. Be careful to measure from the inner side of the bottom. Use a punch (or a small drill bit or a Phillips screwdriver) and a hammer to mark the point. This makes it easier to precisely drill the hole. Be careful not to change the shape of the can doing this by inserting a small block of wood or other object in the can before tapping it.

 Figure 4.36: Mark the hole before drilling.

3. With a small diameter drill bit, make a hole at the center of the plate. Increase the diameter of the hole using bits with an increasing diameter. The hole should fit exactly the N connector. Use the file to smooth the border of the hole and to remove the painting around it in order to ensure a better electrical contact with the connector.

 Figure 4.37: Carefully drill a pilot hole, then use a larger bit to finish the job.

4. Smooth with the file one end of the wire. Tin the wire for around 0.5 cm at the same end helping yourself with the vice.

 Figure 4.38: Tin the end of the wire before soldering.

5. With the soldering iron, tin the central pin of the connector. Keeping the wire vertical with the pliers, solder its tinned side in the hole of the central pin.

 Figure 4.39: Solder the wire to the gold cup on the N connector.

6. Insert a washer and gently screw the nut onto the connector. Trim the wire at 3.05 cm measured from the bottom part of the nut.

 Figure 4.40: The length of the wire is critical.

7. Unscrew the nut from the connector, leaving the washer in place. Insert the connector into the hole of the can. Screw the nut on the connector from inside the can.

 Figure 4.41: Assemble the antenna.

8. Use the pliers or the monkey wrench to screw firmly the nut on the connector. You are done!

 Figure 4.42: Your finished cantenna.

As with the other antenna designs, you should make a weatherproof enclosure for the antenna if you wish to use it outdoors. PVC works well for the can antenna. Insert the entire can in a large PVC tube, and seal the ends with caps and glue. You will need to drill a hole in the side of the tube to accommodate the N connector on the side of the can.

Last Update: 2010-12-02