|
In part one of wireless networking antennas I told you about a basic design, now its time to try and improve on that.
It's time to face facts. When you're dealing with antennas that are already optimally-designed, the only way to get more gain is to increase the size of the receiving area. The main drawback to this is that the amount of gain you get vs. the size of the antenna is not linear. Often, large differences in size will only get you small increases in gain. The exact relationship depends on the antenna design.
With these diminishing returns in mind, I first decided to try to double the antenna  size. Doubling the antenna size would provide the biggest difference, but still be quite small. So, the antenna design that I chose is called a quadquad. It consists of two biquad antennas in a special configuration. Theoretically, the quadquad should give a gain of about 2 to 3dB over the biquad. In tests that I performed, the gain was about 2.5dB better than the biquad.
The next antenna design that I tried consisted of four biquad antennas connected t together in what is known as a phased array. Because of the wave-like nature of radio waves, in order to connect more than one antenna together, it is necessary to phase them in such a way that the waves will add together instead of being destructive. In addition, the impedance must still be observed. In the case of my third antenna, this was accomplished with wires of particular lengths. To keep the dimensions accurate, the four biquad antennas were made with an etched board.
The theoretical gain of this antenna should be about 16dB, which is 4dB more than the biquad. In the case of my phased-array antenna, however, the gain was 1.3dB less than the biquad. This could be due to the fact that my biquad elements were etched instead of made with wire. Still, with this type of antenna, there are many other factors involved, such as the phasing section.
The last directional antenna design uses the biquad as a feed for a  parabolic dish. The gain in this case will depend on the size of the dish used, but can be as high as 30dB or more with a large dish. In my case, I used the biquad with an 18" digital TV dish to get in the range of 20dB of gain. With this setup pointed at an access point with its stock antenna, I was able to achieve a few miles line of sight. I know much better is possible, but for my purposes, I was quite pleased. In my next post, I'll talk about a high-gain omni-directional antenna design.
For even more on this check out part 3
Got a project you've done that you want to share here? Add a comment to this entry.
| 
Re: Build Your Own Wireless Networking Antennas for Longer-Distance 8.0211b/g – Part 2
