Build Your Own Wireless Networking Antennas for Longer-Distance 802.11b/g

Wireless networking is like a home run hit by a baseball player on steroids. They're common enough, but usually good for only a few hundred feet. Fortunately, special wireless networking antennas enable Wi-Fi users to connect to a wireless network from miles away. With 802.11b, the current record for an unamplified 11-mbps connection is 124.9 miles. The antenna that I'm about to describe won't come close to that, but Barry Bonds can't hit a baseball that far either.

For this do-it-yourself (DIY) project, I had three goals. First, build a small-directional, high-gain antenna. Second, build a very high-gain antenna regardless of size. Third, build a high gain omni-directional antenna. This blog entry is about my first goal Subsequent blog entries will describe my second and third goals.

To reach my first goal, I chose an antenna design called a biquad. I researched other antenna designs, of course, but this one is simple and effective. As its name suggests, a biquad consists of two quad-antennas combined. Each side of a quad is ¼ wavelength, thus producing two ¼ wavelength quads that, horizontally, are one full wavelength. Each half of a biquad has an approximate impedance of 100 ohms such that the two quads in parallel make the total impedance 50 ohms, which matches the cable and transmitter.

The plate behind the biquad acts as a signal reflector and ground plane. This ground plane is the "true ground" of the system. It could be earth, or metal attached to a good ground. The distance between the ground plane and the antenna is another factor that changes the impedance of the antenna. Originally, the biquad was designed to be built with a dish. Although I am now using the antenna by itself. The biquad has a theoretical gain of 11.36db, my measurements showed mine was achieving about 10db. I will describe its use with a dish in a later blog entry which can obtain much higher gain.

Want more, check out part 2 of this story