If you look at a typical wireless access point, you will see one or two antennas sticking straight up out of the back of the device. While many people don't realize this, the position of the antenna is no mistake. For example, take a look at Figure 3.
Omni directional radio waves
In the above graphic, you can see that the radio footprint created by an Omni-directional antenna resemble a donut shape. The RF energy is emitted from the antenna and moves outward until it eventually "attenuates," or loses its power. Now, imagine what would happen if the antenna was placed in a horizontal position? Instead of moving outward as in Figure 3, the radio footprint would move vertically.
The makers of the Nintendo Wii had two choices when implementing wireless connectivity in their device. They could either go the cheap route and use a single antenna, or they could spend a few more cents and increase the capabilities of the Wii's wireless networking hardware. Thankfully they went the extra mile and installed two antennas to help ensure the strongest possible signal. Figures 4-6 provide a few shots of these antennas.
Note the orientation of the antennas. It is no mistake that one antenna is positioned vertically and the other is horizontal. There are several technical reasons for this, but it basically all comes down to the simple fact that two antennas in the same orientation generally get the best signal. Since Nintendo has given the end user the option as to how they will place their Wii (laying down or standing up), it makes sense to include one antenna that is oriented horizontally (Figure 5) and a second that is oriented vertically (Figure 6). Due to this thoughtful design, the Wii will be able to dynamically select the antenna with the strongest signal and thus take advantage of its placement.
What antenna to use?
Last year we performed a similar modification to our PSP. As a result, we already had the part and pieces that we needed for this particular "upgrade." In short, we needed two parts — a pigtail and an antenna. The pigtail must have a U.FL connector on the one end, but could have any number of connectors on the opposite end. They key is to ensure your antenna and the pigtail have a matching female/male connector. By separating the components, you can easily upgrade from a 5dBi Omni-direction antenna to a satellite dish, just incase you wanted to connect to an access point on the other side of town. Check out http://froogle.google.com/froogle?q=u.fl%20pigtail for a list of possible solutions (thanks to Drew from alamedawireless.org for this link).