Model and then do Far Field Testing

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.

Acceptance testing in the Far Field for Arrays. 

My test verified the design maximum gain, the azimuth of the maximum gain, steering of both direction, and azimuth, design side-lobes, and the back-to-front ratio.

A calibrated, W&G EMR meter for both the E and H field is used, with the use of a portable tower in the far field at precise predetermined positions. This allowed the for the most suitable method of conducting the test measurements. The analysis and its feedback mechanisms are a major part of K0UO's projects.

Modern programs utilizing NEC2/NEC4 aim to model the loss (absorption of RF) in the ground's electrical conductivity beneath and around an antenna by employing the Sommerfeld-Norton ground model. Older modeling techniques are limited to less effective methods for simulating loss and ground reflections at low angles. To create a skywave, the significant interaction between the antenna and the ground occurs within a radius of 1 to 5 wavelengths from the antenna. Some antennas are more affected by ground losses than others. Nearby objects in the antenna's near field, such as buildings, trees, towers, light poles, other antennas, and fences, significantly influence the outcome, which models may not accurately reflect. Actual patterns in the real world may differ from theoretical models unless the ground's electrical conductivity has been tested.

It is only after you measure the RF radiation pattern of your simulation that you will truly understand what the antenna is doing at your specific location.

I have model all antennas using EZNEC and use HFTA (High Frequency Terrain Analysis) to evaluate the take of angle of the various antennas over real ground

All of my antennas are field-tested to confirm the design specifications, ensuring that the amplitudes and phases of the currents in the radiators match the antenna model. Adjustments are made as needed to achieve maximum gain and an optimal front-to-back ratio. The radiation pattern of an HF antenna is shaped by ground reflection and can also be affected by currents in the support structure. Actual measurements are required to obtain data on gain, beam shape accuracy, slew angle, side-lobe level, and the amplitude of radiation in the minima and rear of the antenna. Predicting these from the amplitudes and phases of the currents in the radiating elements is difficult. If significant differences between the design and actual performance are found, such measurements are useful as adjustments are made.

• K0UO proof tests fall into three categories:

• (1) Comprehensive evaluation of radiation patterns, impedance, and gain for the antenna on 40 & 20 meters.  (160, 80, 30, 17, 15, 10 & 6 meters were considered secondary, but also tested) on the big Rhombics.

• (2) The minimum practical tests provided proof of performance of the installed antenna on 40 meters @ night time "F layer", and Daytime with "D layer absorption". 

• (3) Compares forward gain at the desired azimuth and elevation angle to average gain over the entire hemisphere.

 Wandel & Goltermann E&H Field power density meter with fiber optic cable to PC, the meter-probe is on the crankup 100 foot test tower and uses a fiber cable down to the PC for data collection

• K0UO utilizes Ace HF Pro and IONSUM, which are computer programs that employ the IONCAP prediction method to identify the most appropriate frequency band and necessary antenna gain under specific average conditions. IONSUM stands for IONCAP SUMmary. Propagation predictions are crucial tools for managing HF communications with DX Stations. These predictions provide data to specify the types and operating frequency ranges needed to contact DX stations by adjusting the antenna's take-off angle for maximum signal in the desired direction. They are used to contact DX stations via both long path or short path on the F layer, or to reach North American stations during daytime when the D Layer has higher absorption (160, 80, 60 & 40 meters). Some reflection can occur from the D region, but the radio wave strength diminishes, leading to a significant reduction in the range of radio transmissions during the day on the lower bands.

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A large drone that can handle the payload is what you need, The Drones that can be preprogrammed to fly at precise distances, and height (XYZ) can give you very accurate information on takeoff angles and front to back gain.

Large Drone used to do RF Field testing

The K0UO amateur ham radio antenna range, and testing site has the use of over a thousand acres around the main antennas for far field measurements, using a portable tower or drone loaded with calibrated RF EME survey instruments (used for ham, DOD and Commercial), see the far field test page. https://www.k0uo.com/post/model-and-then-do-far-field-test

An antenna range is a controlled testing environment used to measure and evaluate the performance of antennas.

3D radiation pattern plot at 10 MHz showing the directional gain of an antenna, with colors representing varying decibel levels.

A polar plot illustrating antenna radiation patterns, with key performance metrics such as maximum gain, beamwidth, and front/back ratio detailed in the accompanying analysis window.

The antennas have real gain

Rhombic or Yagis

VK3MO Ian utilizes a stacked rhombic antenna with each leg measuring 8 wavelengths, totaling 1340 meters of radiating wire. The upper rhombic is positioned at 40 meters, while the lower one is at 21 meters. This rhombic antenna achieves a gain of 23 dBi at a take-off angle of 5 degrees on the 20-meter band, aimed towards New York. Modeled using EZNEC, the rhombic demonstrates 3 dB more gain than the 5/5/5/5 yagis. Both the yagis and the rhombic share a take-off angle of 5 degrees, enabling a direct comparison in the direction of New York. Ian observes the 3 dB advantage, confirming the precision of the NEC antenna modeling software.

It can truthfully be said that "a Rhombic antenna occupies more space per dB of gain than any other antenna." The Rhombic is a very high-gain antenna, but it requires a lot of space, and its efficiency when terminated is only about 50%.

An alternative impedance-termination system, used only in a few large broadcast stations with input powers above 50 kW, is known as the re-entrant line termination. Clyde Haehnlen SK developed the specifications for the Voice of America antenna system at the Bethany, OH Relay Station. That re-entrant Rhombic achieved 90% efficiency by re-phasing the power instead of using termination resistors, in this system, the Rhombic is terminated in a transmission line, which is then coupled back to the input through appropriate voltage-matching and phasing networks. This way, the energy in the dissipation line is fed back to the antenna, wasting significantly less than 50% of the energy. The old VOA Bethany site in Ohio had efficiency exceeding 90%. This method feeds back the wasted RF energy "in-phase" into the feeder end of the antenna. For any frequency variation from the stubs, the stub must be retuned.  

I am the only ham or commercial station using re-entrant rhombic line termination equipment, which re-phases the power instead of using termination resistors.

Clyde provided me with design information for re-phasing a few years ago before his passing.

FOR MORE SEE: https://www.k0uo.com/post/rhombic-antenna-testing-in-the-far-field

Models vs. Prototypes: Why Field Adjustment Will Always be Necessary

L. B. Cebik, W4RNL/SK

https://www.antenna2.net/cebik/content/amod/amod130.html

See now at https://antenna2.github.io/cebik/content/amod/modeling.html

A Beginner’s Guide to Modeling with NEC Part 1

For the Best Modeling data on Rhombic antennas see, https://www.antenna2.net/cebik/content/a10/wire/lw4.html

or https://www.antenna2.net/cebik/content/ao/ao11.html

(1) 4Nec2 Rhombic antenna - Variations of the acute angle - Bing video

The K0UO antenna test range site utilizes the 4KS Walz airport, and its surrounding area as a practical learning environment for Scientific, Technical, Engineering, & Mathematics (STEM) antenna projects in an outdoor real-world setting. If group has an a school or University aerospace or antenna research STEM program, let me know.

My Group for RF Site see, https://en.wikipedia.org/wiki/RSI_Corporation

https://www.rsicorp.com/