Where the Current Flows, the Signal Grows

How current flows along an antenna

Not all parts of an antenna radiate equally. The strongest radiation happens where the current is highest and where that current is above ground. That’s why the shape of the current, or the "current taper," is so important when designing or choosing an antenna.

Some antennas are fed at points where the current is naturally strong. Others are fed at points where the current is weak and the voltage is high. Understanding this helps explain why some antennas work better at low heights, and why others need to be raised high to perform well.

Symmetric current-fed vs. voltage-fed antennas

Symmetric current-fed antennas (like center-fed dipoles or off-center-fed wires) are fed in the middle or at a point with strong current. This means:

  • Lower feedpoint voltage
  • Higher efficiency
  • Lower loss in transformers or feedlines
  • Better performance, even when installed at modest height

Voltage-fed antennas (like EFHWs (End-Fed Half Wave) and also some EFOCs (End-Fed Off Center)) are fed near a point where current is low and voltage is high. This means:

  • Very high voltage at the feedpoint
  • High stress on transformers (ununs)
  • Greater chance of power loss and arcing
  • Need for careful installation and better elevation

Examples: EFHW vs. EFOC vs. Doublet

  • An EFHW (End-Fed Half Wave) is fed at the end of the wire, where current is at its minimum and voltage at its maximum. Because the current maximum is far from the feedpoint, you need to install this antenna as high as possible for good performance. It is sensitive to poor grounding, transformer loss, and proximity to other objects.
  • An EFOC (End-Fed Off-Center) antenna is fed closer to a current peak. This makes it easier to match with a 4:1 transformer and allows for better efficiency at lower height. Less voltage stress means fewer problems with arcing or heating.
  • A doublet fed with ladder line is a symmetric antenna, usually center-fed. This places the feedpoint at the current maximum, giving excellent radiation efficiency and low voltage stress. When used with a tuner, it can work well on many bands.

Radiation resistance vs. loss resistance

Antennas have two types of resistance:

  • Radiation resistance is good. It represents the part of the energy that is actually radiated as a signal.
  • Loss resistance is bad. It includes resistance in the wire, transformer, or nearby objects that turns your signal into heat.

You want to maximize radiation resistance and minimize loss resistance. This means placing strong currents in the right place, and using good quality materials and feed systems.

he "Height is Might" Myth

Many hams believe the old saying: “Height is might.” And while that’s often true for dipoles and horizontal antennas, it’s a myth when applied blindly to all antennas — especially verticals.

Raising a vertical antenna might seem like the best way to improve performance, but that’s not always true.

A classic ground-mounted vertical uses the earth as a reference and reflector. It works by launching low-angle radiation with the help of ground currents and image theory. When you raise the entire vertical too high, you lose the ground coupling that helps it radiate efficiently at low angles. Instead, it can start to behave more like a lossy end-fed wire or exhibit unwanted high-angle lobes.

This is why many successful vertical designs keep the vertical element close to the ground but use raised radials to reduce loss — not a raised vertical without a reference plane.

In contrast, dipoles and horizontal wires often benefit from more height, because they depend on having the current maximum as far from ground as possible.

The key message: height helps only when it supports strong current in a position that radiates well — and when it maintains the antenna’s intended geometry.Currents that flow close to the ground tend to lose energy to the soil instead of radiating it. That’s why antennas work better when raised. This is especially important for the current peak:

  • A vertical antenna with raised radials (even just 4) can outperform a vertical with 64 radials on the ground.
  • A dipole or EFOC performs better when its current maximum is above λ/4 from the ground.
  • Raising even part of the antenna can make a noticeable difference.

What Really Makes an Antenna Radiate

The way current flows along your antenna determines how well it radiates. Feeding the antenna at a current maximum is generally more efficient, but sometimes practical constraints lead us to compromise with voltage-fed designs.

Understanding current distribution isn't just theory — it's the difference between being heard and being lost in the noise.

Interested in more technical content like this? Subscribe to our notification list — we only send updates when new articles or blogs are published: https://listmonk.rf.guru/subscription/form

Questions or experiences to share? Feel free to contact RF.Guru or join our feedback group!

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.