Why We Use Simplified Radiation Models — and Not NEC

At RF.Guru, many of our published radiation plots — especially those comparing antenna heights, bands, takeoff angles, or broad configurations — are based on analytical models, not always on full NEC simulations.

That is not because NEC is wrong. NEC is a powerful and valuable modelling tool. But for many of the antennas we design and explain — EFHWs, delta loops, verticals, receive arrays, phased systems, and simple wire antennas — the useful pattern insight is often governed mainly by geometry, height, wavelength, and phasing. For that purpose, analytical models are faster, cleaner, easier to explain, and often just as useful as a full numerical model.

This is especially true at HF, where the real installation is usually full of unknowns: ground, trees, masts, coax routing, common-mode current, counterpoise quality, nearby structures, and imperfect bonding. A highly detailed model is not automatically a more truthful model. Sometimes it is just a more complicated guess.

The goal of many RF.Guru plots is not to claim: “this is exactly what your antenna will do in your garden.” The goal is to show: this is the field behaviour the physics predicts under clean, understandable assumptions.

Pattern Insight Is Not the Same as Installation Prediction

There is an important difference between modelling the antenna concept and predicting a specific installation.

When we show a radiation plot, we are usually trying to explain things like:

• Where the main lobe goes
• How antenna height changes takeoff angle
• Why a low antenna favours NVIS
• Why a higher antenna develops lower-angle lobes
• How phasing changes the pattern of an array
• Why element spacing affects nulls and beamwidth
• How one clean configuration compares with another

For these questions, analytical field equations are often the clearest tool. They show the mechanism directly. They do not hide the lesson behind segmentation settings, ground parameters, convergence warnings, or a false sense of decimal precision.

NEC Simulators: Powerful, Detailed, but Not Always Clearer

Tools such as NEC2, NEC4, EZNEC Pro, 4NEC2, MMANA-GAL, and other electromagnetic solvers are extremely valuable. They are especially useful when geometry, current distribution, impedance, element interaction, and matching details matter.

NEC-based tools can help with:

• Wire segmentation and current distribution
• Element coupling in multi-element antennas
• Feedpoint impedance and SWR estimates
• Trap and loading-coil effects when modelled carefully
• Interaction between nearby conductors
• Ground effects using simplified ground models
• Common-mode paths if the feedline and return path are explicitly included

But that last point is important: NEC only models what you actually put into the model. A normal NEC source is an ideal mathematical feedpoint. It does not automatically include your coax shield, choke, tuner, rig chassis, shack wiring, USB cable, microphone cable, balcony rail, boat bonding system, wet tree, or concrete wall.

This is why a NEC model can show a beautifully balanced antenna while the real installation has RF current flowing on the outside of the coax. In the model, the common-mode path may simply not exist.

All Models Are Idealized — Including NEC

A common misunderstanding is that analytical models are “simple” while NEC models are “real.” That is not quite right.

Both are models. Both use assumptions. Both simplify reality.

An analytical model may assume a clean radiator, ideal ground reflection, simple current distribution, or a defined array factor. A NEC model may assume thin wires, perfect connections, ideal sources, simplified ground, and exact geometry. Neither automatically knows the real-world mess around your antenna.

At HF, that matters a lot. The antenna system often includes things that were never intended to be antennas: coax shields, metal masts, railings, gutters, boat rigging, counterpoise wires, shack wiring, power supplies, and even the operator. If those things carry RF current, they are part of the antenna whether the model includes them or not.

So the question is not: “Is analytical modelling real and NEC fake?” or “Is NEC real and analytical modelling fake?”

The better question is: Which model answers the question most clearly?

Analytical Models: Fast, Clean, and Accurate Enough for Pattern Insight

Analytical models use known electromagnetic relationships to describe field behaviour directly. For example, height-over-ground behaviour, image effects, array factors, and element pattern assumptions can often be expressed with compact equations.

E(θ) ∝ element pattern × height factor × array factor

In many simple cases, this may reduce to expressions similar to:

E(θ) ∝ sin(θ) · cos(k · h · cos(θ))

The exact expression depends on the antenna type, coordinate definition, ground assumption, polarization, and current distribution. The important point is not one magic formula. The important point is that the pattern can often be understood as the combination of:

• The element’s own radiation behaviour
• The effect of height above ground
• The phase difference between direct and reflected fields
• The spacing and phasing of multiple elements
• The wavelength on the band being analysed

This gives immediate insight into takeoff angle, lobes, nulls, beamwidth, and broadside or end-fire behaviour. For many educational and comparative plots, that is exactly the information we need.

When Analytical Modelling Is Better Than NEC

We often prefer analytical models when the goal is to compare broad behaviour rather than to predict every detail of a physical installation.

Analytical modelling is especially useful when we want to:

• Explore height effects across multiple HF bands
• Compare takeoff angles for NVIS, regional work, and DX
• Show how a loop, vertical, dipole, or EFHW behaves in broad terms
• Visualize how low-angle and high-angle radiation change with height
• Study phased receive arrays such as EchoTriad or QuadraTus
• Demonstrate the effect of spacing and phasing in array systems
• Generate fast comparisons without changing dozens of NEC parameters
• Explain why the pattern changes, not merely show that it changes

In these situations, NEC’s extra detail may add runtime and complexity without adding useful insight. A more detailed model is only better if the added detail is accurate and relevant.

If the goal is to understand why a low dipole radiates upward, or why an antenna at greater height develops lower-angle lobes, or why array spacing creates nulls, then analytical models often communicate the answer better.

When NEC Is the Better Tool

We still use NEC and NEC-like tools where they truly matter. Analytical models are not a replacement for detailed modelling in every situation.

NEC is often the better tool for:

• Feedpoint impedance estimation
• SWR behaviour across frequency
• Current distribution along complex wire shapes
• Element coupling in Yagis, phased systems, and close-spaced arrays
• Effects of bends, slopes, offsets, and asymmetric geometry
• Trap, loading-coil, and matching-network studies
• Estimating the effect of nearby conductors when they are known
• Testing whether a clean analytical assumption still holds in a more detailed geometry

But even here, NEC’s results are only as good as the model. If the real antenna is installed near a tree, brick wall, balcony rail, wet roof, boat mast, coax run, or hidden wiring that is not correctly represented, then the NEC result is still only a controlled approximation.

NEC can be very precise about the wrong reality.

Common Mode: The Part Many Models Forget

One of the biggest practical differences between clean models and real HF antennas is common-mode current.

In an analytical plot, the feed system is normally assumed to be ideal. In a simple NEC model, the source is also often ideal. That means the coax shield, choke, tuner, rig chassis, shack wiring, and operator are absent unless deliberately added.

In the real world, especially at HF, the coax can become part of the antenna. This can happen when:

• The antenna is electrically unbalanced
• The counterpoise or radial system is inadequate
• The choke impedance is too low
• The feedline runs through the antenna’s near field
• The installation is asymmetric
• The antenna is mounted close to metalwork, buildings, or ground

Common-mode current can change the pattern, alter the impedance, increase receive noise, create RF in the shack, and make the antenna appear to work differently from the model.

This does not make analytical plots useless. It simply means they show the behaviour of the intended antenna, not every accidental conductor connected to it.

A model can show the intended radiator. Measurements reveal whether the feedline has quietly joined the antenna system.

Why the Differences Are Often Small for Pattern Shape

For many simple antennas, the broad far-field pattern is dominated by large-scale geometry: height, orientation, wavelength, and phase. These are exactly the things analytical models capture well.

For example:

• A low horizontal HF antenna will still favour high-angle radiation
• A higher horizontal antenna will still develop lower-angle lobes
• A vertical will still depend heavily on its return system and ground environment
• A phased array will still form lobes and nulls based on spacing and phase
• A loop’s broad behaviour will still follow its current distribution and orientation

NEC may refine the numbers. It may shift a null slightly, change a lobe by a fraction of a dB, or show an impedance effect the analytical model does not attempt to predict. Those refinements are valuable when they answer the question being asked.

But for visualizing the main pattern behaviour, the simplified model often tells the story more clearly.

What Our Plots Should Be Used For

RF.Guru plots are best understood as engineering insight plots. They are there to help you understand the antenna, not to pretend that your exact garden, balcony, boat, rooftop, mast, feedline, ground, and weather conditions have been measured by software.

Use them to understand:

• Which direction the antenna favours
• Whether the pattern is high-angle, low-angle, broadside, or omnidirectional
• How height changes the useful radiation angle
• How band changes affect the same physical antenna
• How spacing and phasing shape an array
• Why one design choice is likely better than another

Do not use them as a promise of exact gain, SWR, bandwidth, front-to-back ratio, or received signal level in your installation.

So Why Not Always Use NEC?

Because using a more complex tool does not automatically produce a better explanation.

If the purpose is to explain a physical principle, an analytical model is often superior. It is transparent. It is adjustable. It runs instantly. It shows the relationship between wavelength, height, phase, and pattern without burying the lesson inside a geometry file.

If the purpose is to refine a specific build, then NEC becomes more useful. But even then, it must be used with discipline: realistic geometry, realistic ground assumptions, realistic losses, realistic feedline behaviour, and verification by measurement.

The best engineering workflow is often:

• Use analytical models to understand the physics
• Use NEC to test specific geometry and impedance behaviour
• Build the antenna with proper choking and feedline control
• Measure the real result
• Adjust based on what the installation actually does

Bottom Line

For most RF.Guru educational radiation plots, the pattern is governed primarily by geometry, height, wavelength, and phase. Analytical models capture these effects with excellent clarity and speed.

That is why our default visualizations are often analytical:

• They are scientifically grounded
• They are fast and transparent
• They make assumptions visible
• They are easy to compare across bands and heights
• They show the physics instead of hiding it
• They help you understand the antenna, not merely simulate it

NEC remains valuable. We use it where it adds real value: impedance, current distribution, element coupling, geometry refinement, and design verification. But NEC is not automatically more truthful just because it is more detailed.

If you want to verify, refine, and tweak with NEC — excellent. We do that too. But for many pattern-level questions, the answer is already visible in the math. Analytical modelling shows the principle; NEC checks the implementation; measurement proves the installation.

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