The Yagi reborn for 2010 - OWL Yagi is here

Choosing a Yagi can be quite a dilemma for many hams, if an OWA (Optimised Wideband Array) 50 Ohm Yagi is chosen, good bandwidth is the result along with simple feeding arrangements too. Another added bonus is the pattern in any modelling software package you see, is pretty much what you get.

With Low impedance examples, gain and F/B is better, bandwidth suffers but in most cases, still provides sufficient coverage of the band(s) wanted so this is not too much of a problem. The issue is matching. First of all, exact losses for a matching arrangement are not easily measured so actual final (built) performance is not known. The next is the impact the matching arrangement has on the pattern and performance. While most optimisation (software) tools provide an adjustment in impedance equal to the effects a matching arrangement will have on the antenna, they do not model the effects on pattern or performance the matching arrangements physical presence has.

As the impedance of a Yagi drops further, performance increases more so but the antenna becomes very unstable, especially when we reach near optimum levels, around 12.5Ohm and lower. What if an antenna could be developed with an input impedance of 12.5Ohm which retained the performance capabilities of that impedance level but adopted the wideband characteristics of the OWA too? What if it maintained the pattern symmetry and cleanliness the OWA 50 Ohm Yagi was renowned for?  What if it had other performance enhancing characteristics not seen in a Yagi before to ensure the highest levels of forward gain while maintaining Front to Back Ratio (F/B) and a matching arrangement proven to have very limited impact on the final pattern?

Enter the Optimised Wideband Low Impedance (OWL) Yagi

 

 a 7el 50MHz G0KSC OWL Yagi with a boom length of just 7.85 metre producing 12.84dBi at 50.250MHz

 

The SWR curve of the OWL looks more like an OWA 50 Ohm Yagi than a 12.5Ohm Yagi

 

 

Another comparison (below) presents a DK7ZB 11el 144MHz 28Ohm Yagi, a YU7EF 12el 50Ohm Yagi, and the G0KSC 11el 12.5Ohm OWL Yagi.

Antenna             length          Gain               F/B             Worst Lobe         144-145MHz Bandwidth

DK7ZB 11el            7.075M        15.83dBi          23.6dB         13.32dB                1.23:1

YU7EF 12el            7.260M        15.92dBi          20.21dB       16.59dB                2.14:1

G0KSC 12el OWL   7.123M        15.84dBi          27.93dB        17.13dBi               1.1:1

Comparison notes:

• All comparisions were conducted within EZNEC Pro/4 and the latest NEC4.1 R3 Calculation engine
• Segmentation density used was 28 per half wave in each antenna
• Test Frequency 144.300MHz
• 'Worst Lobe' being the largest unwanted forward lobe in the Azimuth planebigger number is better
• Dimensions for both YU7EF and DK7ZB model from the respective website (10mm element versions)
• G0KSC OWL using 1/2inch dipole and 3/8 inch elements

While the plots below do not look like some of those published in the designers websites exactly, I beleive this goes part way to prove my belief that you can not simply change the diameter size of elements within an antenna  and expect to get the same antenna results (many element diameter options are presented for 'the same antenna' on each site). In my opinion, an antenna has to be optimised in both X and Y planes for each element diameter in order to achieve the best possible results each time. For each set of element diameters, a new gain, SWR and F/B figures will result. As stated above, these comparisons are based on 10mm diameter elements as the G0KSC 12el OWL uses 3.8 inch (9.525mm) elements and these versions of both the YU7EF 12el and DK7ZB 11el where similar in both boom length and element diameter.

All antennas have good gain and this gain follows the boom length of each respective antenna with the YU7EF being longest and having highest gain, then the G0KSC OWL with the shortest being the DK7ZB. However, it is not gain we are looking at here. I beleive if you focus (when optimising) on all other attributes, the gain will come. Afteral, anyone can produce an antenna with gain alone using a Yagi optimiser after only 5 minutes right? What takes time and patience is maintaining that gain while modeling a wideband antenna. Wide bandwidth is important as it results in a less critical (build dimensions) designs and a much more stable antenna when built, less susceptible to Rain, Snow and Ice. The G0KSC OWL maintains high levels of gain while producing the very wide bandwidth characterisctics of the LFA Yagi and at the same time, suppressing unwanted lobes and maintaining F/B. All in all a very stable, very quite antenna!

Next are the comparison plots. Note the symmetry within the OWL Antenna.

DK7ZB Azimuth plane at 144.300MHz

 

DK7ZB Elivation plane at 144.300MHz

 

DK7ZB SWR Plot (NEC4.1)

 

YU7EF Azimuth plane plot

 

YU7EF Elevation plot

 

 

The above example hopefully give the reader an idea of the incredible performance capabilities if the OWL Yagi by G0KSC. A 25 page article explaining how this has been achieved and why it has never been achieved before will be published in DUBUS magazine in the first issue 2010.

If you are interested in building one ahead of their release, email me with your requirement.

 

Justin G0KSC