PowAbeam Antennas offer a range of high-performance VHF and UHF Yagi antennas conceived by Derek Hilleard (G4CQM) and hand-built to order by The DX Shop in the UK.
Advanced Optimized Wideband Antenna (AOWA) style and low-Q Yagis, designed for wider bandwidth and improved stability during rain, snow, or wet weather conditions.
Derek is one of the very few Radio Amateurs to own the powerful design software from Brian Beezley (K6STI) both YO7 and AO 'professional' versions.
YO uses a conjugate-gradient optimizer that combines the Fletcher-Reeves and Polak-Ribiere methods.
1926 came invention of the Yagi-Uda Antenna, a major breakthrough in VHF/UHF communication.
In a recent paper written by Kunio Sawaya
(Department of Communications Engineering), Tohoku University (Japan), describes a typical concept design of that time. It had three reflector elements, one exciter and twenty director elements. it was centered on 68MHz...
| Concept Yagi-Uda seen in AOP | Concept Yagi-Uda Characteristics |
|---|---|
| |
| Concept Yagi-Uda Azimuth | Concept Yagi-Uda Elevation |
| |
For several decades now radio enthusiasts have made efforts to refine yagi designs using a range of tools. Pioneering amateurs like Günter Hoch had access to a test range belonging to the German Post Office. He carried out extensive tests on VHF/UHF yagi designs in a bid to quantify his measurements and make improvements. This led to a range of DL6WU designs which were adopted widely across the globe.
The Yagi-Uda antenna has a frequency response similar to that of a Low Pass Filter. Bandwidth has to be a high priority in design consideration along with a clean and stable polar pattern.
Seen below an animation of characteristics comparing different designs. Some past designs were gain optimized, unfortunately suffering instability during weather and proximity stress. Example 2M7N50 shows this narrow bandwidth, however slightly longer boom redesigned 2M7N50LY solves this limitation. Other designs such as the high performance BVO3WL50 by DJ9BV can be seen as very narrow band, subject to instability in wet conditions.
| Animation showing bandwidth evolution of the AOWA |
|---|
 |
Until this point in time all designs have one thing in common, designed by humans! Yes, optimizing often used, but guided by an experienced designer knowing precisely those best qualities to adopt and enhance. Tools previously included those such as Genetic Algorithm and Particle Swarm models, again requiring an experienced designer to oversee.
Work in progress to be continued...
