Cobweb Antenna in Amateur Radio

The Cobweb antenna (originally called the “Cobwebb” after its inventor, Steve Webb G3TPW) is a compact, multi-band HF antenna that provides omnidirectional, horizontally polarized radiation. It is highly popular among hams with limited space—such as small urban lots or rooftops—because it offers full-size dipole performance in a fraction of the footprint.

How It Works

At its core, a Cobweb is simply a nested set of half-wave dipoles (usually covering 20m, 17m, 15m, 12m, and 10m) that have been bent into squares and mounted on an X-shaped frame made of fiberglass spreaders.

Bending a standard half-wave dipole into a square significantly reduces its physical size, but it also alters its electrical properties. The ends of the dipole are brought close together (separated by an insulator), which drops the feedpoint impedance from a standard 73 ohms down to roughly 12.5 ohms.

Because all the dipoles are fed from a single central feedpoint, there are two distinct design approaches to match this low impedance back to a 50-ohm transceiver.

The Two Main Designs

1. The Original G3TPW “Cobwebb”

• The Design: Uses twin-lead speaker wire or figure-8 cable to create folded dipoles.
• The Match: A folded dipole naturally multiplies the impedance by four. By multiplying the 12.5-ohm feedpoint by four, the antenna natively achieves a near-perfect 50-ohm match.
• The Catch: It requires precise shorting of the twin-lead ends and can be frustrating to tune because the wire’s velocity factor heavily impacts the resonance.

2. The G3TXQ Variation (The Homebrewer’s Choice)

• The Design: Steve Hunt (G3TXQ) redesigned the antenna using standard single-wire elements instead of twin-lead.
• The Match: Because single wires remain at 12.5 ohms, this design uses a 1:4 Guanella current balun at the feedpoint to step the impedance up to 50 ohms.
• The Catch: You have to wind a dual-core balun, but it is vastly easier to build, tune, and prune than the original twin-lead version.

Performance Characteristics

Because the elements are packed tightly together, many hams assume the Cobweb is a compromised or “dummy load” antenna. In reality, it is highly efficient.

Attribute	Characteristic
Footprint	Roughly 8.5 × 8.5 feet for a 20m–10m version.
Radiation Pattern	Nearly omnidirectional. The square shape fills in the deep “nulls” found at the ends of a straight wire dipole. No rotator is needed.
Polarization	Horizontal. This makes it notably quieter on receive than vertical antennas, as it picks up less man-made electrical noise.
Gain	~0 dBd. It provides practically identical gain to a full-size, straight half-wave dipole mounted at the same height.
Bandwidth	Wide enough to cover the entire band on 20m through 12m without a tuner. 10m usually requires choosing either the CW/Data or SSB portion.