Rhombic and V Beam Design
- skylarkcolo
- Nov 20, 2021
- 11 min read
Updated: Aug 26
The rhombic is the largest and most refined of the long-wire antennas, consisting of two Vs, open-end to open-end. The result is 4 wires contributing aligned lobes for higher gain and narrower beamwidth. The rhombic suppresses unwanted sidelobes better than the V antenna.
The site emphasizes the scientific method: model → build → far-field test → refine
Good symmetry is of vital importance for the performance of this antenna. The width of the antenna's main lobe is determined by the angles q and a, often referred to as tilt and apex angle. In general, the wider the rhombic (greater a and smaller q) the wider the beam and vice versa. Of coarse q and a are linked since the sum of half the tilt angle and apex angles is always 90 degrees: q/2 + a/2 = 90
Effective Antenna Aperture Calculator below is useful. Antenna gain G is directly proportional to the antenna aperture A and is increased by means of focusing radiation in only one direction while reducing radiation in all other directions. So, the narrower the width of the beam, the higher the antenna gain.
a 14dBd antenna on 7 MHz is Ae 6,014.99624 m²
a 14dBd antenna on 14 MHz is Ae 1,503.74976 m²
Capture area or Effective Aperture is determined by antenna gain and the wavelength, not by antenna physical size.
The big antennas use wire rope, not copper wire to carry the weight and to keep wire sag lower. The most suitable metal is relevant in relation to the mechanical properties of the install. For rhombic antennas the concern should be using maximum size wire/cable rather than the conductivity of the material. Larger is also better for RF skin effect, and a traveling wave antenna will be terminated anyway.
The old books say, "The gain of a rhombic with side lengths of four to five wavelengths is over 40 times that of a half wave dipole. About one half of this gain is realized by using two wave lengths to each of the four sides" From the old DoD Book, EI8IC Reprint
NOTE, Don't underestimate the performance of the Rhombic, unless you have personally built and used one. Because of their excessive size (area) covering many acres, you see their real advantage of thousands of feet of wire in the air, which creates receive signal diversity, by capturing signals at different times and different angles, vastly eliminating fading QSB, and firing out the transmitted RF in the same way. Traveling wave antennas are very unique and unlike many other antenna in common use, modeling will not show this major advantage.
Keep in mind that K0UO is comparing rhombics to large stacked single band yagis beams that were previously used on 195-foot rotating towers at K0UO, and has tested both yagis and rhombics on the RSI Corp antenna test range. "Rhombics bets Beams"
Now using NEC5 (newer MOM algorithm) from Lawerence Livermore Lab, but it still won't show the real performance of the Rhombic.
A word about modeling: You no longer need the latest modeling software, as it's design is rapidly evolving with Artificial Intelligence.
We started integrating AI with modeling in 2024, and now have developed an AI analysis platform focused on antenna performance and specific parameters. Be cautious and invest time in setting the correct parameters for your "AI platform".
One high end paid AI platform is now using AN-SOF, which is a robust simulation engine designed for the modeling and analysis of complex antenna systems and radiating structures.
Gain total spatial awareness of your antenna’s performance with immersive 3D rendering. AN-3D Pattern utilizes colored mesh and surface mapping to visualize radiation lobes with professional clarity.
Creating a well-designed platform using scientific and engineering knowledge is crucial.
Relying solely on ChatGPT is not the solution at all!
Modeling Traveling-wave Arrays
AN-SOF provides significantly higher simulation accuracy than legacy NEC software (such as NEC-2 or NEC-4) when modeling large traveling-wave antennas like Rhombics, Beverages, and long V-beams. Its performance advantage stems from how its computational engine handles wire geometry, acute angles, and ground physics
Only AN-SOF is somewhat capable of accurately simulating large traveling-wave antennas, including Rhombics, Beverages, and extensive V-arrays. This is achieved through its advanced Conformal Method of Moments (CMoM) engine, complemented by comprehensive Sommerfeld ground physics.
The Exact Kernel Advantage: Legacy NEC tools struggle with localized "current bunches" near lumped loads or sharp transitions. Because AN-SOF calculates currents over the actual tubular surface of the wire (the Exact Kernel) rather than an infinitely thin line, it more precisely models how the current transitions from a traveling wave into a termination load.
Exact Kernel vs. Thin-Wire Approximation
NEC Limitation: Legacy NEC engines rely on the thin-wire kernel approximation, assuming electric current flows along an infinitely thin line down the wire axis. Near lumped termination loads (such as a 600Ω resistor) or abrupt geometry transitions, this approximation creates non-physical current spikes ("current bunches").
AN-SOF Advantage: Operates on the Conformal Method of Moments (CMoM) with an Exact Kernel, integrating currents over the true cylindrical surface area (2πa) of the wire. This accurately captures the smooth transition from a progressive traveling wave into the termination load.
Apex Junction Stability
NEC Limitation: Traveling-wave arrays like Rhombics and V-beams feature sharp acute apex angles where wires meet at narrow corners. In NEC-2/4, closely spaced segments near acute corners trigger mathematical breakdown, miscalculating mutual coupling.
AN-SOF Advantage: CMoM satisfies boundary conditions across acute angles and close wire spacings without numerical instabilities or artificial "bent wire" artifacts.
Ground Physics & Near-Field Losses
NEC Limitation: Low-height traveling-wave antennas (especially Beverages) depend heavily on ground losses. Older NEC tools often use Reflection Coefficient Approximations (RCA), which fail in the near-field and oversimplify ground return currents.
AN-SOF Advantage: Implements the Sommerfeld-Wait ground model, providing accurate calculations for near-field ground absorption, input impedance, and low-angle radiation patterns over lossy earth.
Importance of Far Field Testing in HF Traveling-Wave Arrays
Performing actual Far Field testing remains a crucial requirement for numerous high-frequency (HF) Traveling-wave array projects. This testing methodology is not merely a formality; rather, it serves as an essential component in validating the performance and efficiency of the arrays. The Far Field testing process involves measuring the electromagnetic fields produced by the array at a considerable distance, where the effects of the antenna's near-field influence diminish, allowing for a more accurate assessment of its radiative characteristics.
Understanding Far Field Testing
The significance of Far Field testing lies in its ability to provide critical insights into the radiation patterns, gain, and overall efficiency of the HF Traveling-wave arrays. In the context of HF frequencies, where wavelengths can be relatively long, the precision in measuring the antenna's performance becomes even more vital. Far Field testing enables engineers and researchers to capture data that reflects how the array will perform in real-world scenarios, including various atmospheric conditions and operational environments.
Applications and Benefits
The applications of Far Field testing in HF Traveling-wave arrays are vast, spanning military communications, broadcasting, and scientific research. For instance, in military applications, the reliability of communication systems can significantly impact operational effectiveness. Thus, ensuring that the Traveling-wave arrays can perform optimally at long distances is paramount. Similarly, in broadcasting, achieving the desired coverage area and signal quality is essential for reaching audiences effectively. Moreover, Far Field testing provides a benchmark for comparing different array designs and configurations. By analyzing the results, engineers can make informed decisions regarding modifications or enhancements to the array structure, ultimately leading to improved performance metrics. This iterative process of testing and refinement helps in achieving arrays that not only meet but exceed operational specifications.
Challenges and Considerations
Despite its importance, conducting Far Field testing presents certain challenges. The setup for such tests can be complex, requiring specialized equipment and controlled environments to minimize interference from external sources. Additionally, the interpretation of the data gathered during testing can be intricate, necessitating a deep understanding of electromagnetic theory and antenna behavior. Furthermore, advancements in simulation technologies have led some to question the necessity of physical testing. While simulations can provide valuable preliminary insights, they cannot entirely replace the need for actual Far Field measurements. The real-world variables that affect antenna performance can only be accurately captured through empirical testing.
Conclusion
In conclusion, the practice of performing actual Far Field testing remains indispensable for many HF Traveling-wave array projects. It not only validates the theoretical models but also ensures that the arrays can operate effectively in practical applications. As technology continues to evolve, the methodologies surrounding Far Field testing will likely adapt, but the fundamental need for this rigorous testing process will persist in ensuring the reliability and efficiency of HF communication systems.
The K0UO & RSI Corp platform, which uses Artificial Intelligence to design traveling wave and other antennas, is much more reliable, and completes the process in about 5% of the time required by traditional modeling programs. Setting it up requires time, similar to the initial setup of the original computer modeling software. It's easy to make mistakes by assuming artificial intelligence can operate without errors.
After designing something, we now have the advantage of using our outdoor testing range to validate the results. I consider it essential to confirm results and assess performance in real-world conditions. My team has collaborated with several commercial clients to do just that.
I started with calculators, and some of us are old enough to remember using slide rules and pencils, before moving to computer modeling. It's astonishing to see how far we've come, and in a few more years, like it or not AI will further revolutionize antenna design.
A rhombic with 4 wavelength legs is, of course, twice as long overall as a V with 4 wavelength legs, but the width is about the same, since the same angle-based construction is involved. The terminating impedance of a rhombic (600 to 900 Ohms) is in series with the collinear array wires. Therefore, we see far less difference between the gain of the unterminated and the terminated versions. However, we can achieve very high front-to-back ratios.
For commercial service, the major failing of all long-wire technology was the high level of the sidelobes, clearly evident on all of the patterns. The correct V or rhombic angle might combine two or more long-wire lobes, but it did little to suppress the other lobes in the long-wire pattern. For amateur use of the side-lobes can be useful for making QSOs.
When an antenna is good at what it does, we can count on efforts to make the good even better. For narrow-beamwidth point-to-point communications, the rhombic is very good. One very old technique to improve performance somewhat is the use of multiple wires in each side of the rhombic. They come together at the feedpoint and at the terminating resistor end, but spread vertically where the facing Vs are widest. Some claims about the technique will prove correct, such as the addition of a small increment of gain. However, other claims may turn out to have other foundations than the use of multiple wires.
I only use single wire designs at my site, less work. If I want more gain, I just make the antenna longer, however some of you don't have the space. A 3 wire arrays only gives about 1 dB gain. But you can enlarge the average wire diameter, the gain does increase by a numerically noticeable amount. Also the array of front-to-back values are better..
Laport developed a scheme for using closely spaced rhomboid structures in parallel. The centerlines for each of the independent rhomboids fed in parallel are offset from each other. The technique will offer a small gain advantage over the single-wire rhombic, but will reduce sidelobes by a very significant amount.
Fig. 10 provides a 3-dimensional pattern for the rhombic with 10 wavelength legs. It reveals that the terminated rhombic exerts the most control over the morass of small lobes that populate the overall radiation pattern Also the.relationships between the value of the terminating resistor and the feedpoint impedance that bear on the smoothness of SWR curves that cover a 2:1 frequency range. The termination provides considerable more bandwidth up to 4 to 1.
A V-Beam is just 1/2 of a rhombic. The V array derives directly from the single long-wire antenna. In fact, a V array is nothing more than two single long-wires connected at a feedpoint junction and fed in series. The V array makes use of one of the problems for a single wire: the two main lobes do not come completely together to form a single lobe. The V array turns the problem into an advantage. If we angle each leg of the V beam in just the right way, we can get two of the lobes--one from each leg--to point in the same direction and let their gain levels add. Fig. 1 shows the outline of how we obtain a true bi-directional unterminated array from 2 long-wire antennas.
The U.S. Army/Navy made an Rhombic antenna calculators that I have, were developed during the 40's for Army use in field design of antennas. They are large and made of plastic (plexiglass) and are circular type slide rules. It allowed you to calculate tilt angles for antenna wavelength (in frequency), dimensions, etc. I have one but can't find it, if you have one please sent me a photo.
SEE Above: Now you need a non inductive terminating resistor
Initial and later studies in rhombic antennas provide more complex equations to calculate compromises where the elevation and the V'ing angle do not match. Some of the equations appear in nomographic form. For example, one such nomograph appears in the ARRL chapter on long-wire and traveling-wave antennas, as well as in articles and text devoted specifically to the design of rhombic antennas. (See the Harper volume in the reference list.) Such nomographs are capable of guiding the rhombic designer to excellent results.
Some programs are limited to 500 segments. Tthe longer rhombics require up to 1000 segments, if we adhere to our 20-segment per wavelength standard. However, a full 6 wavelength-per-leg rhombic comes in at under the 500 segment mark.
We may use the selected height and the associated values of angle A to design any number of rhombic antennas. In fact, we can use a simple long-wire as the starting point. NEC allows us, via the GM command, to rotate the wire by the required number of degrees dictated by the value of angle A for a given wire length. (Programs like EZNEC use a different but equally effective method of rotating wires.) Hence, we can easily create a V and find its coordinates. From those coordinates, we can complete the rhombic by doubling the overall length and bringing 2 new wires back together--or almost together.
The use of angle A assures us of lobe direction coincidence and gain addition along the centerline of the antenna. We may then let NEC calculate the gain and actual elevation angle for the selected antenna height over any selected soil. Before we close this series, we shall find that NEC's handling of rhombic design and at least one nomographically based design turn out to be virtually identical. Traditional methods are quite accurate, but in the present age of computerized antenna design, the modeling process is often simpler. As we have seen from our experience with single long-wire and V antennas, the modeling method also provides ready supplementary information, for example about sidelobes, feedpoint impedances, and power dissipation in the load resistance of terminated antennas.
I am now using the biggest HF Re-entrant Rhombic arrays, and they are the highest forward gain HF antennas with its 90% efficiency, now with very high gain, and low noise receive characteristics. So, the Rhombic Arrays can beat the massive stacked HF beam arrays that I had up before.
Now days the biggest gun contest or DX stations would use a
4, over 4, over 4, stacked 40 and 20 meters Yagis at ~180 ft is very high-end (gain often ~10–13 dBd real-world, depending on phasing/spacing ~0.5–0.75λ vertical).
However a properly sized rhombic at 100 ft apex (long legs) can offer higher forward gain (3–5 dB more in modeled comparisons at low angles), vastly better F/B, with multi-band capability. If using a K0UO 90% efficiency re-phasing system, you would gain even more gain, and no moving towers to wait to turn or parts to breaks! An added bonus is diversity TX & RX, reducing fading.
How to build a 20 meter Rhombic
e Geometries Become Complex A Rhombic Case Study
L. B. Cebik, W4RNL/SK
Also See
Models vs. Prototypes: Why Field Adjustment Will Always be Necessary
L. B. Cebik, W4RNL/SK
https://www.translatorscafe.com/unit-converter/en-US/calculator/effective-antenna-aperture/
Historic Preservation: The K0UO station diligently preserves and uses components and insulators from renowned, historic radio arrays, including those from W6AM (Don Wallace), W7YRV Roy, BBC, Voice of America (VOA), and many others.
"The K0UO station is unlike any other ham station globally," making it truly unique as a Big Gun Mega Station. It is one of the few capable of constructing and utilizing very large Rhombic and V Beams, along with a variety of other antennas and AI. K0UO features the largest operational HF wire antenna in the world.
"I hope others will carry on the tradition, and art of building the large Rhombic Arrays in the future". It is truly the "PHD" of wire antennas.
The RSI Corp and K0UO antenna test range site in Kansas
73
General Steve Walz, V31KW/K0UO
SEE ALL BLOGS Here, & Just Skip the first few pages, and go to the Blog List
A wealth of information throughout your blogs and thank you for letting me be at your site last year it truly has the world's largest wire HF antennas.
Keep up the work
Wow, you really need to read every one of his pages incredible