OWA (Optimized Wideband Antenna) Yagi Design - G4CQM

Optimized Wideband Antenna - 2M Band OWA Dipole
Optimized Wideband Antenna - 2M Band OWA Dipole

Author G4CQM 26-08-2018

Designing High Performance yagis for Amateur Radio is not as easy as you might first think! There are many variables and an almost infinite number of permutations of element position, length, and diameter. Each set of build dimensions gives rise to a completely different design. Some designs however are much better than others!

In recent years the quest for novel/gimmick driven elements has caused confusion in the ranks, so it's time apply some science!

Incorporation of both rural and residential local noise temperatures into the VE7BQH Antenna Tables (Gnumeric file only 126333 bytes!) is a huge step forward in highlighting those yagi antenna designs that really are a cut above the rest!

 

During the early 90's...

The OWA (Optimized Wideband Antenna) is an antenna employing a feed-point matching system conceived by Professor Jim Breakall, WA3FET (Penn State University), and delivers an increase in feed-point impedance whilst substantially improving on the available/useable VSWR bandwidth. Above is a 2M Band OWA Dipole example based on Jim's original 80M implementation, and configured in K6STI's AOP (professional version) software! Antenna file (.ANT) using Symbolic Dimensions can be seen here... OWADIPOLE.ANT.txt

Raising feed-point impedance is particularly useful in yagi design where mutual coupling and loading effects can drop feed-point impedance to very low values, and then become difficult to match whilst also incurring greater losses!

Note that to more accurately simulate the original OWA antenna concept, the 144MHz version requires wires (elements) of only 0.5mm diameter in proportion to the increase in frequency and shorter wavelength. Flanking the Split Dipole (the driven element) there are two shorter parasitic elements spaced some 0.01λ from the driven element, without this configuration the resultant polar pattern becomes distorted (not symmetrical). Those familiar with yagi design will see these parasitic elements in the same context as the yagis first director (D1) which enhances gain in the forward direction.

In realized OWA yagi designs only one parasitic element is required because some forward gain is of help and not a hindrance, suggested spacing distance of around 0.05λ is required. However, with large diameter elements this spacing has to be increased accordingly!

The OWA Dipole is truly remarkable, an example below simply demonstrates that an increase in impedance is possible whilst also significantly lowering the average Q-factor, with noteable improvement in operational bandwidth!...

 

<<< Split Dipole Vs OWA Dipole >>>
2M Band Split Dipole (0.5mm element dia) in AOP2M Band OWA Dipole (0.5mm element dia) in AOP
2M Band Split Dipole (0.5mm element dia) in AOP2M Band OWA Dipole (0.5mm element dia) in AOP
Total FieldTotal Field
2M Band Split Dipole (0.5mm element dia) VSWR2M Band OWA Dipole (0.5mm element dia) VSWR
2M Band Split Dipole VSWR 140-150MHz2M Band OWA Dipole VSWR 140-150MHz
Split Dipole Q-factor (average 8.9)
140 - 150MHz
OWA Dipole Q-factor (average 2.7) resonant HF of band!
140 - 150MHz
Split Dipole Q-factor (average 8.9)OWA Dipole Q-factor (average 2.7) resonant HF of band!

 

Designing the Advanced OWA (AOWA) yagi, an historical insight...

Early in 1994 my research and experiments focused on choosing a suitable yagi design for the 2M Band, with particular attention paid to the driven element type. From a commercial point of view ease of construction and repeatability were of paramount importance!

After trying/testing a Hairpin Match detailed in the ARRL VHF/UHF handbook and encountering build problems along with poor/inconsistent results, time for something different! It was then that I moved to the concept of Direct Feed and simple Split Dipole driven element. This idea was just starting to become popular and adopted by others. Hairpins are highly reactive located right on the feed-point and so tiny variations in construction give rise to volatility!

To begin with I opted for YAGIMAX by the late Lew Gordon (K4VX) to design the first PowAbeam Antennas 2M0818SK 8 element 2M Band yagi. Software by Lew is very easy to use and true enough delivered a stable and reliable design. However, YAGIMAX is somewhat limited optimizing for gain and F/B only, and without being able to control the front/rear region. Despite these limitations 2M0818SK has a remarkably flat frequency response. Note the OWA style close spacing between the Split Dipole driven element and D1!...

 

G4CQM 2M0818SK OWA style (1994)

PowAbeam Antennas 2M0818SK 8 element 2M Band yagi seen in YAGIMAX
PowAbeam Antennas 2M0818SK 8 element 2M Band yagi seen in YAGIMAX
GAIN, VSWR, & F/B Vs FREQUENCY

 

K6STI's YO7 Professional

A few years later (1999/2000) I purchased K6STI's YO7 Professional and AO Professional version software for my professional work as a consultant at Communication Aerials Ltd of Westbury Wiltshire. This enabled me to refine and calibrate my yagi designs against NEC-2...

The original G4CQM PowAbeam 8 element yagi (2M0818SK) certainly qualifies as an OWA style yagi. However, compare overall performance with modern WA9XX AOWA (lower temperature and better G/Ta in a noisy residential environment simulation) and you will see the difference!

 

Original G4CQM PowAbeam 8 element yagi refined in K6STI's YO7 Pro
Original G4CQM PowAbeam 8 element yagi refined in K6STI's YO7 Pro
2M0818SK OWA style very low average Q-factor
Q-factor
E-PlaneH-Plane
E-PlaneH-Plane
Residential performance as per new interactive VE7BQH Antenna Tables
Single yagi...
2M0818SK in AGTC LITE (residential)

 

DJ9BV and the high gain distraction!

DJ9BV designs soon became popular in the mid to late 90's, and they did perform very well. These designs employed a low element boom density/wide spacing. Some of my own best DX was worked with the BVO2-3WL 50Ω direct feed design! However, there was a problem, they were sensitive to their surroundings and detuned in wet weather! Several Radio Amateurs have provided feedback regarding this problem.
The reason: Because these designs had a very high average Q-factor, and high levels of reactance at the HF end of the band. In short, they were gain optimized yagis. BVO2 designs had a unique current distribution profile, I tried to mimic this in the PowAbeam Antennas designs at that time...

 

BVO2 designs had a unique current distribution profile
BVO2 designs had a unique current distribution profile
BVO designs very high average Q-factor!
BVO designs very high average Q-factor!
G4CQM gain optimized 2M-2.5WL design 1999
1999 PowAbeam Antennas leaflet
2M-2.5WL current distribution profile like BVO2 designs!
BVO2 designs had a unique current distribution profile, I tried to mimic this in the PowAbeam Antennas designs at that time
2M-2.5WL very high average Q-factor!
Gain optimized yagis suffer a very high average Q-factor!

 

My return to yagi designing in 2008!

When I returned to designing yagis for Ham Radio in 2008 things had moved on! The first of my so called new designs were still based on the gain optimized concept as seen in the 2M7N50 design below... Meanwhile, Pop YU7EF had established a range of unique 50Ω low noise designs that had a lower average Q-factor than the DJ9BV designs. As a result Pop's designs were more stable and had gained considerable favour!

I soon discovered some new techniques (not OWA style) to design low Q long yagis as seen below in the 2M7N50LY example, the boom length is slightly longer and position of the Split Dipole driven element and D1 has changed, still wide spacing throughout. Note the much lower average Q-factor and improved F/R power ratio too!

 

G4CQM 2M7N50 gain optimized design
The first of my so called new designs were still based on the gain optimized concept as seen in the 2M7N50 design
Still a very high avearge Q-factor!
G4CQM 2M7N50LY low average Q-factor design with improved F/R
I soon discovered some new techniques to design low Q long yagis as seen in the 2M7N50LY example
Note the much lower average Q-factor!

 

Wave Antennas and the Advanced OWA (AOWA) yagi!

During the early months of 2013 I decided to fully embrace 50Ω Direct Feed - Low Q - Low Noise - OWA style! An excellent example of what defines an Advanced OWA (AOWA) design can be seen below in Wave Antennas WA9XX... It has very close spacing between the Split Dipole driven element and D1, OWA style. Meanwhile the parasitic elements are spaced in a specially contrived sequence in order to deliver a tight/clean pattern in both E and H Planes. In the words of Pop YU7EF, this yagi design has carefully balanced parameters!

In conclusion my research reveals that Advanced OWA (AOWA) yagi designs having six or more elements in total are more than capable of outperforming those yagi designs employing novel/gimmick driven elements. The critical part is getting the Split Dipole driven element and D1 spacing just right in relation to the other elements, so delivering the real Optimized Wideband Antenna (OWA) benefits!

WA9XX 1.79λ AOWA

WA9XX AOWA in K6STI's YO7 Pro
WA9XX AOWA in K6STI's YO7 Pro
WA9XX SWR
WA9XX SWR
Shallow Q-factor gradient like that of a highly stable DL6WU yagi
Q-factor
E-PlaneH-Plane
E-PlaneH-Plane
Residential performance as per new interactive VE7BQH Antenna Tables
Single yagi...
WA9XX in AGTC LITE (residential)
Residential performance as per new interactive VE7BQH Antenna Tables
4 x yagi...
4 x WA9XX in AGTC LITE (residential)

 

Antenna File...

WA9XX.ANT.txt

 

Wave Antennas...

  • THESE YAGI ANTENNA DESIGNS ARE NOT FOR COMMERCIAL USE OF ANY KIND WITHOUT PRIOR CONSENT!
  • Private experimenters are free to use these designs for their own personal enlightenment. However, no guarantee or warranty is offered or implied.
  • MY WEBSITE DOES NOT USE COOKIES, EXTERNAL LINKS MIGHT!
Flag Counter