Why We Use Simplified Radiation Models — and Not NEC

At RF.Guru, many of our published radiation plots — especially those comparing different antenna heights, bands, or configurations — are based on analytical models, not full NEC (Numerical Electromagnetics Code) simulations. That’s not because NEC is wrong or inadequate — it's because for the types of antennas we design (EFHWs, delta loops, verticals, receive arrays, etc.), the difference in far-field results is minimal, while the clarity and speed of simplified models are far superior.

Let’s unpack that.

NEC Simulators: Accurate, Complex, and Overkill for Pattern Insight

Tools like NEC2, NEC4, or commercial solvers (EZNEC Pro, 4NEC2, MMANA-GAL, etc.) are valuable for modelling fine geometric detail:

  • Wire segmentation
  • Element coupling
  • Coax and common-mode behaviour
  • Ground conductivity and dielectric layers

But all NEC engines (even NEC4) rely on assumptions:

  • Ground is flat (even with Sommerfeld modeling)
  • Near-field coupling to nearby objects (trees, buildings, clutter) is ignored
  • Radiation pattern is only calculated in the far field
  • The source is idealized and doesn't reflect practical feedline routing

For basic pattern shape (elevation takeoff angle, omnidirectionality, beamwidth), the impact of these refinements is minor. Often within a fraction of a dB.

Analytical Models: Fast, Clean, and Accurate Enough

We use classic field equations like:

E(θ) ∝ sin(θ) · cos(k · h · cos(θ))

This gives:

  • Elevation pattern of a vertical element over ground
  • Dependence on antenna height and frequency
  • Clean insight into take-off angle, nulls, and lobes

Similarly, for azimuth we approximate the broadside or omnidirectional characteristics using simple cos(φ) envelopes or array factor sums. These are not toy models — they are grounded in electromagnetic field theory, and match NEC results very closely for most real-world purposes.

When Analytical > NEC

We prefer analytical models when we want to:

  • Explore height effects across bands
  • Compare broadband behaviour of loop, vertical, or EFHW designs
  • Visualize takeoff angles for NVIS vs DX
  • Design phased arrays (like the EchoTriad or QuadraTus) with tunable spacing

In these cases, NEC's extra complexity adds runtime, not clarity.

What NEC Still Does Best

We do use NEC where it truly matters:

  • Input impedance and SWR prediction
  • Modeling of choke placement, matching networks, or trap tuning

But even then, NEC’s results are only as good as the realism of your model — and NEC doesn’t know your actual tree line or brick wall.

Bottom Line

For most of our antennas, the radiation pattern is governed by geometry, height, and wavelength. These simplified models capture that with stunning accuracy — and they do it instantly, without endless tweaking or segmentation errors.

That’s why our default visualizations are analytical:

  • They are scientifically grounded
  • They are transparent and adjustable
  • And most importantly — they make you understand the antenna, not just simulate it

If you want to tweak and verify with NEC — great, we often do that too. But for most cases, you’ll find that the answers are already in the math.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.