Half-Wave Verticals Without a Ground Field

The useful distinction is not “radials or no radials.” It is whether the antenna already includes both sides of its intended RF current path. A centre-fed vertical dipole does. A quarter-wave monopole uses a radial, counterpoise or earth system as its other side. An end-fed half-wave can avoid the large radial field familiar from a ground-mounted monopole, but it cannot avoid Maxwell: current still returns through something.

Begin With the Antenna You Actually Built

“Half-wave vertical” is a geometry description, not a complete feed-system description. Three installations that look similar from a distance can be electrically different:

• Centre-fed vertical dipole: two approximately quarter-wave arms form the intended differential current path. The feedline should not become a third arm.
• End-fed half-wave: the generator is connected through a matching network near a current minimum and voltage maximum. The network transforms the high complex feed impedance, while a deliberate or incidental conductor completes the low-side path.
• Quarter-wave monopole: the vertical conductor is only one side of the intended antenna. Radials, an elevated counterpoise, a vehicle body, a conductive roof or an engineered earth system forms the other side.

These arrangements cannot inherit one another’s radial advice. The current maximum of a centre-fed half-wave dipole is near its feedpoint; the end-fed half-wave is fed near a current minimum; the base-fed quarter-wave monopole carries high current into its ground or counterpoise system. That difference is why a radial field is central to one design and optional—or even an unintended parasitic structure—in another.

A Complete Vertical Dipole Does Not Need a Monopole Ground Field

In the ideal centre-fed case, equal and opposite RF currents flow into the two dipole arms. The lower arm is not “ground”; it is part of the radiating structure. The antenna can therefore operate without forcing its intended differential current through soil or through a buried radial field.

That does not make the feedline irrelevant. The outside of a coaxial shield is a separate conductor from the differential path inside the cable. As Roy Lewallen, W7EL, demonstrated, asymmetry or an additional low-impedance path can place common-mode current on that exterior conductor. The feedline, mast and station wiring then join the radiating system and can change impedance, pattern and accessible RF voltage.

A current choke is useful when its measured common-mode impedance at the installed location reduces that unwanted current without unacceptable differential loss or RF stress. It does not create the missing half of a centre-fed dipole; the lower arm already does that.

An End-Fed Half-Wave Still Needs a Return Path

The end of a half-wave wire is a low-current, high-voltage region, not a zero-current escape hatch. The matching network has two terminals, and current entering one terminal must leave the other. The return may be a deliberate counterpoise, a defined section of coax exterior before a choke, a support or bonding conductor, displacement current to nearby objects and soil, or an uncontrolled mixture of station wiring and surroundings.

High feedpoint impedance often means lower feed current for a given accepted power, but it does not prove negligible ground loss. Combining a nominal multi-kilohm feed impedance with an arbitrary ground resistance treats a distributed coupled system as one series resistor. In practice, the end impedance is complex and installation-dependent, the transformer changes current and voltage, and soil loss arises from distributed electric and magnetic fields as well as any identifiable conductor current.

This is why “no ground field required” is defensible while “no return path required” is not. A short intentional conductor may be enough in one installation; in another, the coax exterior or nearby metal dominates. Measure the current paths instead of inferring them from the wire’s nominal electrical length.

Quarter-Wave Radial Results Do Not Transfer Automatically

Rudy Severns, N6LF, measured how radial number, length, symmetry, elevation and soil conditions affect ground-mounted and elevated quarter-wave vertical systems. Those experiments show why the immediate ground system can recover power that would otherwise be dissipated near a monopole base. They also show that sparse elevated systems can be sensitive to imbalance and environment.

That evidence does not say that any radial field improves any vertical. A full vertical dipole already has its second radiating arm. Adding wires beneath it may do little, but they can also couple to the lower arm, alter current distribution, change feed impedance, modify the pattern or provide a new common-mode path. The effect has to be modelled or measured for the installed geometry.

For a defined conductor carrying RMS current through a defined effective loss resistance, P_loss = I²R remains useful. Real soil is a distributed lossy dielectric, however. Its conductivity and permittivity, moisture, frequency and the antenna’s near fields determine the actual dissipation. One current sample at the connector is not a soil-loss measurement.

Height and Soil Still Shape the Pattern

Removing a monopole radial requirement does not remove the Earth. A vertical dipole or end-fed half-wave above real ground interacts with its image and with lossy soil. The lower-end height, total vertical span, soil constants, slope, nearby structures and common-mode conductors affect feed impedance and the elevation pattern.

ITU-R BS.705 treats ground conductivity, topography and surrounding structures as explicit pattern variables for HF antennas. The current NEC family likewise models wires above real ground through Sommerfeld-ground methods. Neither supports one universal minimum height, fixed efficiency penalty or “fraction of a dB” radial effect.

A lower end close to soil can increase electric-field coupling and loss, but raising the antenna can also change the pattern and feed impedance rather than producing a simple monotonic improvement. The required height comes from the target coverage, mechanical site, exposure assessment and measured or converged model—not from a universal 0.05λ or 0.1λ rule.

SWR Improvement Is Evidence of a Changed System

When a wire called a radial or counterpoise improves SWR, it has changed the antenna system. It may have stabilised the matching-network reference, supplied a deliberate return path, changed common-mode current, altered the radiator’s effective electrical length, or coupled directly into the near field. The SWR change alone cannot tell which happened.

Likewise, reduced RF in the shack after adding a choke does not prove more radiated power. It shows that a current path changed. That may be exactly the desired result, but field strength, accepted power, feed-system loss and pattern remain separate quantities.

Transformer Choice Is a Load-and-Stress Decision

It is not valid to declare that half-wave verticals on particular upper-HF bands work better without a transformer. End impedance, matching ratio and transformer loss depend on the actual wire, frequency, environment, winding topology, parasitics and complex load. A feedline section can transform impedance too, but it does not make loss or common mode disappear.

Characterise a matching assembly with representative complex loads at declared planes. Record input impedance, accepted-to-delivered power, voltage, current, temperature, waveform and duty cycle. If a transformer, transmission-line section or tuner meets those requirements, its name is secondary to its measured result.

Prove the Installed Current Paths

A useful comparison keeps the radiator, support, feedline route, matching unit, choke and surrounding conductors fixed while changing only the proposed ground or return arrangement.

• Calibrate or de-embed the VNA to a declared feedpoint plane and save R, X and reflection phase, not SWR alone.
• Measure current on both intended radiator conductors where accessible and at several positions on the coax exterior, mast, counterpoise and bonding conductors.
• Record accepted and delivered power at defined planes, plus matching-unit and choke temperature under the intended waveform and duty cycle.
• Use a validated full-geometry model or a controlled field-strength A/B/A test to check pattern-sensitive conclusions.
• Repeat after soil moisture, cable routing or nearby structures change if those variables are material.

High voltage can exist at the ends and matching network of a half-wave radiator even when feed current is modest. Keep conductors and enclosures inaccessible during transmission, provide suitable clearance and insulation, inhibit the transmitter before adjustment, and complete the applicable RF-exposure assessment. A radial decision is not an electrical-safety or lightning-bonding decision; those systems have separate requirements.

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