11-El.-2-m-50-Ohm-V-Yagi

As it has become more to focus on the noise figure than on the gain of Yagi-antennas I decided to develop some models with these fundamentals.

But before introducing some of the new antennas we should look on the design rules used for these Yagi types. The older DK7ZB-Yagis with 28-Ohm have a higher gain but a bigger first side lobe than the new "low noise" Yagis. In the 90’s I have introduced low impedance 12,5-Ohm-Yagis with a close spaced reflector for high F/B and F/R, but the focus was not primary a high bandwidth. The focus was for extreme high gain and high F/B. The types had only a length up to 1,5 lambda. The reason was that I did not believe that long boom Yagis would have an advantage with this concept. Meanwhile G0KSC has shown that it is possible to use the 12,5-Ohm-design for excellent patterns and great bandwidth.

Here is a short introduction for the different design principles and their fundamentals. For the 28-Ohm-DK7ZB-Yagis read here:  Longyagi-principles

Some years ago YU7EF presented a new type of Yagis with the "low-noise" principle. That means extreme reduced side lobes for minimizing the receiving of unwanted signals ("noise"). Therefore he changed the travelling wave zone and the end zone of the Yagi. He shortened the directors continuously; the last directors are very short. But there are very low currents in the last directors, which leads to less efficiency and some reduced gain. You cannot get it all! The second YU7EF-principle is the 50-Ohm-direct feed, that means the intrinsic impedance of the Yagi is 50 Ohm. The Yagis can be built with open dipoles or with a 200-Ohm-folded dipole and a half wave balun. If you want to know more, here is the website with a lot of models for various bands: YU7EF

Other very impressive 50-Ohm-direct feed-Yagis with a complete different design (FLOWA) and real 50-Ohm-AOWAs (Advanced Optimized Wideband Antennas) are presented by  G4CQM  

These new DK7ZB-OWL-Yagis use the best compromise between three design principles:

DK7ZB: The 12,5-Ohm-Yagi design for high gain, easy matching and simple to build open dipole with the well known and well proved  DK7ZB-Match or a 50-Ohm folded dipole for direct connection of a 50-Ohm-coax cable. This is not an intrinsic 50-Ohm-direct feed, but the folded dipole is used as a match element 12,5/50 Ohm. This was introduced in the 90’s in some articles for the German Ham-Magazine "FUNKAMATEUR".

YU7EF: Director-chain for good suppressed of the side lobes in the elevation- and azimuth-plane. But I have not extremely reduced the reactance -j X for the directors as YU7EF does in his designs. The consequence is more gain. Remember that you can get the same G/T with an extreme high gain and moderate side lobes or reduced gain and extremely suppressed side lobes. I prefer the first method, but this is discussible.

G0KSC: The extreme narrow spaced reflector and a close first director in the driver cell for wide bandwidth (OWL). The lower gain with the YU7EF-director chain can be compensated widely with the now slightly longer travelling wave zone. G0KSC-OWL-Yagis

Remarkable is the high current in director 1 (typical for 50-Ohm-direct-feed-Yagis), the system radiator and D 1 (elements 2 and 3) act as a coupled system like the "open-sleeve" model. The lower currents, especially in D 3, D 8 and D 9 (elements 5, 10 and 11) are the cause for the better pattern but with some reduced gain.

For the development I use the tools with which I have worked for many years with a very good result. As you know you must tell each program what you want it to do. It is possible to design the OWL-Yagis with the programs YO and EZNEC +5. The picture shows the development of the 8,65 m long 144-MHz-OWL- Yagi with 14 elements. Against other statements: YO is able to find not only high-gain Yagis with great first sidelobe. With reduced gain and the right handling you can also optimize the bandwidth and the side lobe patterns. Here is a screenshot of the 14-El.-OWL- Yagi (elevation plane).

The stable parameters (gain, impedance, and pattern) over a wide range are the benefit of the OWL-12,5-Ohm concept.  

The first who used a bent reflector for improving the pattern of a Yagi was UA9TC. The picture shows a cutout of a 13-El.-UA9TC-Yagi. The second attribute of the Yagis is the very low Ta with YU7EF-style directors and the great bandwidth. But the gain is significant lower than with more conventional designed Yagis.

These Yagis are promoted by G0KSC as "Opposing-Phase-Element-Driven-System". I have investigated several designs and it seems that the attributes of the Yagis with bent reflectors and bent radiators are nearly the same. I have replaced the UA9TC-reflector by an OP-DES-radiator. Pattern and impedance are identical. For the practical construction the right angle bent radiator is the better choice in my eyes for tuning the system.

The LFA (Loop Fed Array) is another type of feeding system with bent radiator. It is a flat loop that has not only the task to improve the patterns. It acts as a transformation system in the range of 1:4 to 50 Ohm for the low impedance structure of the Yagi, which is the secret for the higher gain as with the two systems described above.

The first who used a V-bending of the radiator was K6STI.

A modified version with a stretched middle part and bent ends was made by DG7YBN. Meanwhile he has published several Yagis with the V-radiator, see here:  DG7YBN

Designing of V-Yagis

The radiator with a linear middle part has two advantages in comparison with the original K6STI one. The first is the easier mechanical contstruction, the second is the better simulation with NEC-ll-programs. The reason is the characteristic that sources for the feed are only possible in the middle of a wire.

Blue arrows: First sidelobe

Red arrows: Unwanted radiation +/- 90° of the boom

The backward lobes for a better F/R can be reduced when changing a 50-Ohm-design to a lower impedance. That is the key for the OWL-Yagis and for the DK7ZB-28-Ohm-Yagis.

A classic Yagi has a deep zero in the range of the red arrows. All bent radiators (including the LFA) have that unwanted radiation in the azimuth plane +90° and -90°. Of cause these lobes should be as low as possible. A greater angle of the V gives a better F/R but more radiation in the section marked by the red arrows, a lower angle will reduce that anwanted radiation, but gives a worse F/R. A have made a lot investigations for the best compromize, it seems to be an angle between 5° and 10°.

When designing a Yagi for a V-radiator the best starting point may be a classic Yagi with 28 Ohm impedance (sorry if I bother you always with that impedance....), because the angle for raising the impedance is in the range of 5°-10°. The G/T is influenced by the gain of the Yagi in relation to the sidelobes and the F/R and that will give the best results.