To further increase gain, a horn can be added to the front of the can. This antenna is mostly cardboard, the can itself is a cardboard with metal lining milk tub, the horn is made from aluminium backed cardboard. This was obtained as an A0 size sheet from an art shop, nothing special! To make a horn to suit the 92mm aperture of the milk tub, simply draw two concentric arcs using the following dimensions:-

Inner radius = 85.2mm

Outer radius = 316mm

Rotation angle = 194 degrees.

These dimension should provide a gain of around 16dBi

In order to attempt to smooth out the junction between the can and the horn and to ensure electrical continuity, I used self adhesive, conductive copper tape. Brief tests showed this antenna to produce the expected extra gain and significantly increased directivity.

Results:

Click to enlarge!

On the left is the signal with just a dog food tin cantenna, the stronger signal is using the above cardboard horn! The Orinoco client claims an excellent signal, Windows XP signal meter shows 4 bars and a signal strength of "Very Good"! This signal strength is better than I get 20m from the AP when inside the building housing it! The trees in the way are now in full leaf too, I don't see how I can really improve on this.

In fact there's so much gain, I still got a usable signal with this antenna inside the Travelodge, simply stuck on to the TV and pointing through the walls:-