Directional Wire Antennas for 20–40M: From Bobtail to Half-Square

Directional wire antennas are an excellent solution for hams who want to maximize gain and directivity without resorting to large towers or rotatable Yagis. On the 20, 30, and 40 meter bands, several time-tested designs exist, each with unique strengths and trade-offs.

The Half-Square: Elegant Simplicity

The half-square antenna is arguably the most practical and easiest-to-install directional wire antenna for 20–40 meters. It consists of two quarter-wave vertical elements connected at the top by a half-wave horizontal wire. The pattern is directional broadside to the wire, with a very low takeoff angle (~20–30°), making it ideal for DX.

At RF.Guru, we offer a monoband half-square fed with an end-fed transformer (68:1 or 56:1 depending on band), which simplifies installation even further. Instead of a corner-fed or center-fed system requiring balanced line, this version allows easy coax feed from one end, with the other end elevated. The result: low-angle, vertically polarized DX performance with minimal fuss.

Bobtail Curtain: The Gain Beast

The bobtail curtain extends the half-square into a three-vertical system. With three quarter-wave verticals spaced half a wavelength apart and connected by top wires, this array has increased broadside gain (up to ~6 dBi) and retains low-angle vertical polarization.

Its main drawback is the size and mechanical complexity: it requires three high supports and a full wavelength of horizontal space. Feedpoint is typically at the bottom center vertical.

Extended Double Zepp (EDZ): Horizontal High-Gain

The extended double Zepp is a ~1.25 wavelength horizontal doublet fed at the center, typically with open wire. It provides broadside gain of ~6.5 dBi at low angles when mounted high (preferably >0.6λ above ground).

Pros:

  • Simple construction
  • High gain in broadside direction

Cons:

  • Needs significant height to achieve low-angle performance
  • Horizontal polarization is more susceptible to urban noise
  • Requires tuner and balanced feed

Rhombic: When Space Isn’t a Problem

The rhombic antenna is a large, diamond-shaped wire array that offers extremely narrow beamwidth, very low takeoff angle, and strong forward gain. It can be terminated (unidirectional) or unterminated (bidirectional).

While performance is unmatched for fixed high-gain operation, it requires huge real estate and is rarely practical outside of rural or field-day deployments.

Lazy H and Double Half-Square: Honorable Mentions

  • Lazy H: Two dipoles spaced vertically and fed in phase, offering moderate directional gain when mounted high. Good for fixed installations.
  • Double Half-Square: Two phased half-squares can be used for switchable direction or sharper pattern control. Needs more supports but offers good flexibility.

Why the Half-Square Often Wins

Among all these, the half-square stands out due to:

  • Ease of construction (especially end-fed versions)
  • Very low angle radiation with vertical polarization
  • Only two supports needed
  • Minimal ground interaction issues compared to vertical monopoles

It's monoband by nature, but that's a small price to pay for effortless DX performance.

Conclusion: If you want a compact, effective, and low-noise directional antenna for 20, 30, or 40 meters, the half-square remains king. For those who have more space and want more gain, the bobtail curtain or EDZ offer alternatives. But for no fuzz easy maintenance, an end-fed half-square is hard to beat.

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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.