Feedpoint placement on 1/4-wave or 5/8-wave

At RF.Guru, we like to do things differently — but always with a reason.

When you compare one of our 1/4-wave or 5/8-wave verticals to standard commercial designs, you might notice something subtle but significant: our feedpoints are not placed at the very bottom. Instead, they are positioned higher up along the radiator, typically about 30 cm above the physical base of the antenna. That small change has a big effect on radiation efficiency and performance.

Why Feedpoint Placement Matters

In a classic ground-mounted vertical, the feedpoint is placed at the bottom of the radiator, right above the radial system. The current distribution in such an antenna starts at its maximum near the feedpoint and tapers off toward the top. However, the lowest section of the radiator, especially the portion within 30–50 cm of the ground or radial hub, contributes very little to far-field radiation. This is due to two factors:

  1. Radiation efficiency scales with height: Radiation from a vertical element is a function of current magnitude × height above ground. The portion closest to the ground has minimal radiation resistance and maximal reactive coupling to ground proximity or radial level.
  2. Current maxima are poorly utilized: The strongest current near the base is being wasted in a region where it can hardly radiate due to ground proximity or radial level.

By shifting the feedpoint upward on the radiator, we deliberately exclude this ineffective lower section from the radiating structure. That 30 cm stub below the radial plane still serves as mechanical support, but it no longer carries the primary RF current responsible for radiation.

The Benefit: Lower Radiation Angle, Higher Efficiency

When the feedpoint is raised, the current maximum is shifted upward. This adjustment has two immediate benefits:

  • Lower elevation angle: The effective height of the radiating current increases, which improves far-field launch angles. In practical terms, this translates to a stronger low-angle radiation lobe, ideal for long-distance (DX) communication.
  • Less ground loss: Ground-induced loss is significantly higher near the earth's surface. By reducing current in the lowest portion of the antenna, you reduce I^2R losses coupled into the ground. This improves the antenna's radiation efficiency.

Application to 1/4-wave and 5/8-wave Verticals

This technique works for both 1/4-wave and 5/8-wave verticals:

  • In a 1/4-wave vertical, the feedpoint shift shortens the radiator slightly but improves the current distribution, leading to stronger low-angle radiation.
  • In a 5/8-wave vertical, which already exhibits a lower radiation angle due to its extended length, shifting the feedpoint enhances this effect by concentrating radiating current higher up.

Combined with our use of large-diameter (35 mm) marine-grade aluminum tubing, which supports smoother current taper and reduces ohmic losses, these verticals exhibit:

  • Higher forward gain at low elevation angles
  • Cleaner SWR curves
  • More effective real-world performance

The RF.Guru Philosophy

We don’t just build antennas to match textbook formulas — we engineer them for real-world performance. Feedpoint position is one of those often-overlooked details that separates good antennas from great ones.

So if you notice our verticals are a bit shorter than expected, it’s not an accident. It’s the result of deliberate feedpoint positioning, optimized current taper, and a design focused on maximum radiated power at useful angles.

Because for us, efficiency isn't a marketing term — it's a measurable goal.

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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.