Stan, the originator of all this can be found here ... http://www.usbwifi.orcon.net.nz/
Give the web site a thorough reading, lot's of valuable info here. This is where you will get detailed description on how to put one of these together. 

This web page shows how I built mine. This is an endorsement from one RVer to all others who need a reliable way of 'hooking up' to a campground WiFi network when the signal is far away or weak. THIS GADGET WORKS

After many frustrating attempts at trying to pick up weak WiFi signals in various campgrounds I did an extensive search on the Internet and found Stan's site. His solution to a vexing problem looked so simple I had to try it. Imagine my surprise when I picked up nine other signals from my laptop using a $6 scoop. The built in antenna in most laptops is very weak, good for local in-house networks only. An external USB WiFi Wireless Adapter (dongle) can double the range, specially if its at the end of a two meter USB cable hanging out the window. Starting with the dongle and a little bit of ingenuity this inexpensive dish solution almost guarantees a clear reception from any WiFi network within sight.

Note: This is not an antenna, its a dish that concentrates the signal to the real antenna inside the dongle.
 
My first attempt using a $6 scoop and duct tape. (it works well as is)

Stan explains it clearly in this picture http://www.usbwifi.orcon.net.nz/usbscoop.jpg

My scoop is 240 mm wide and 50 mm deep so the focal point is 72 mm from the bottom centre of the dish. (240 x 240) divided by (16 x 50). The dongle's antenna pictured above has to be within the focal point of the dish. Depending on the dish dimensions you may have to use other methods to hold the antenna in the focal spot. It doesn't have to be pretty.

For the mathematically challenged or when using an odd shaped dish this other method works well. http://www.usbwifi.orcon.net.nz/finger.jpg

The USB Wireless Adapter can be found in any electronic store or online: DONGLE 
If you can't find a skimmer, it can be bought online: SPIDER SCOOP

This is really a simple design that can be improvised with material found at hand, no hard fast rules except for the focal length. I made the stand with a wire coat hanger, it's a temporary fix for now. The dish is light enough to be attached to any improvised pole or mast if you need to raise it above ground clutter. I've been playing around with a suction cup attached to a swivel that would easily stick to any smooth surface like windows or fibreglass siding found on most RVs.

All it needs now is a coat of black paint to go from cookware to geekware.

Note the plastic doughnut ring used to firm up the mesh. 
The finished dish has two of these with the mesh sandwiched in-between.

http://www.usbwifi.orcon.net.nz/99.jpg   (original design idea & instructions)

Painted and  looking almost 'store bought'

 
The second picture is the final product. It is made from a camera tripod head and a suction cup, this allows me to but it anywhere on the RV.

This one I put together using an old camera flash reflector. The dongle comes with it's own little stand and I simply used an elastic band to hold it together. It works amazingly well.

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