What is the hentenna's gain and impedance?

Builders commonly report about 5 dBd of gain, similar to a three-element Yagi, with a feed-point resistance in the region of 50 to 70 ohms so it can be fed with 50 ohm coax.

Is a hentenna directional?

It is bidirectional: it radiates broadside to the plane of the loop, front and back, with horizontal polarisation when mounted upright.

Is a hentenna horizontally or vertically polarised?

Mounted upright it is horizontally polarised. Turned 90 degrees on its side it is vertically polarised, and tilted to about 45 degrees it is a mixed slant compromise costing roughly 3 dB against either.

Does a hentenna need a balun?

A 1:1 current balun or a few turns of coax as a choke at the feed point is good practice to keep common-mode current off the feedline, even though some builders report working designs without one.

GazLabs › Homebrew Antennas › Hentenna calculator

Hentenna Calculator

Q: What are the dimensions of a hentenna?

The classic proportions are a rectangle one half wavelength high and one sixth of a wavelength wide, with a horizontal feed bar roughly one tenth of a wavelength up from the bottom. Real antennas are trimmed a few percent shorter for conductor end effect.

Enter a frequency and get the width, height and feed-bar position for a homebrew hentenna, plus a cut list if you are building it from copper pipe or aluminium tube.

Frequency (MHz)

Band preset

Shortening factor

Conductor

Fitting allowance (mm)

Feed gap (mm)

Dimensions are centre-to-centre of the conductor.

Classic proportions are width λ/6, height λ/2 and feed bar about λ/10 from the bottom, scaled by the shortening factor. Treat the result as a starting point and trim against an antenna analyser or NanoVNA.

Polarisation: vertical or horizontal?

Horizontal as drawn · vertical when turned on its side

Upright (as drawn)Horizontal polarisation Turned 90° on its sideVertical polarisation Tilted about 45°Slant: mixed, theoretically about 3 dB down on either PatternBidirectional, broadside to the plane of the loop

Rotating the loop within its own plane changes the polarisation but leaves the broadside direction the same. Re-check SWR after turning it, because the feed point and nearby metal change.

See the simulated radiation pattern for upright, 45° and sideways →

Compromise installation

Pick the mode you use most. SSB, CW and FT8 on 6 m, 2 m and 70 cm are conventionally horizontal, so mount it upright. For FM voice, repeaters and packet or APRS, which are vertical, turn it on its side.
Mixed traffic? Tilt the loop to about 45°. It loses roughly 3 dB against either polarisation in theory, far less than the worst-case cross-polar loss, which is often quoted at up to about 20 dB on line-of-sight paths.
Make it swappable. Fit the loop to the mast with a single quick-release bolt so you can turn it between upright and sideways in a minute or two.
Use a non-metallic mast section. Keep a fibreglass or PVC section behind the loop, because a metal mast close to it shifts the tuning and distorts the pattern.
Height beats polarisation on HF. On HF skywave paths polarisation hardly matters. Put the loop as high as you can and keep it clear of buildings and wiring.
Indoors or in a loft? Reflections inside buildings make polarisation less predictable, so either orientation is a reasonable compromise at VHF and UHF.

What is a hentenna?

The hentenna is an asymmetrical double rectangle (ADR) loop. It was developed by Japanese six-metre amateurs in the 1970s and reached a wider audience through QST in 1982. "Hen" is Japanese for odd or unusual, which sums up a loop that is fed from a bar partway up one rectangle instead of from the middle of a side.

The lower part of the structure acts as a matching section, which is why a single feed point lands close to 50 ohms without a separate matching network. Builders commonly report around 5 dBd of gain, broadly comparable with a three-element Yagi, and a low take-off angle. The pattern is bidirectional, broadside to the loop, and the antenna is horizontally polarised when mounted upright. Because it is a single rigid loop it is easy to rotate on a mast.

Building one

2 m copper pipe

A 15 mm (½ in) copper pipe build with solder fittings needs four elbows, two tees and end caps, and works with no feed tuning at all if the dimensions are followed closely. Published 2 m builds land at around 39–40 in tall and 12–13 in wide.

Wire for HF and 6 m

Wire hentennas on 6 m are the traditional form. Use spreaders of bamboo, fibreglass or PVC conduit, and keep the wire taut so the shape holds in the wind.

Feed and choke

Feed across the gap in the centre of the bar. A 1:1 current balun, or 6–8 turns of coax wound into a coil close to the feed point, helps keep common-mode current off the feedline.

Tuning

Slide the feed bar up or down to move the impedance, checking SWR with an analyser. Reported 2 m examples reach roughly 1.2–1.4:1 with broad bandwidth, though some builders measure higher resistance and need to experiment.

Safety: keep every antenna well clear of overhead power lines, including when it is being raised or lowered, and do not rotate a loop in a position where it could drop onto people or cables. Make sure pipe and fittings are fully dry and ventilated when soldering.

Hentenna FAQ

What are the dimensions of a hentenna?

One half wavelength high, one sixth of a wavelength wide, with the feed bar roughly one tenth of a wavelength up from the bottom. Trim the result a few percent shorter for end effect, which is what the shortening factor does.

What impedance does it have?

Commonly 50–70 Ω, so ordinary 50 Ω coax works. Individual builds vary with conductor thickness, feed-bar position and nearby metalwork.

Can I build one for HF?

Yes, but size is the limit. On 20 m the loop is about 10 m tall, so most builders use it from 10 m upwards, or on VHF/UHF where it is compact.

Horizontal or vertical polarisation?

Mounted upright, as shown, it is horizontally polarised. Turn the loop 90° on its side for vertical polarisation. The broadside direction stays the same, but re-check the SWR. See the polarisation guide above for compromise installs.

Where do these proportions come from?

They are the widely quoted standard ratios for the design, backed up by published 2 m copper-pipe builds that landed within a few percent of the scaled result. See the sources below.

More antenna tools

Browse the homebrew antenna guide, or open another design at the frequency you entered above:

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Sources

IW5EDI, "The Hentenna" (2 m copper-pipe build): iw5edi.com
EA7AHG, "Hentenna" (2 m SWR and impedance measurements): sites.google.com/site/ea7ahg
VU3NSH, "Hentenna – An ADR Antenna" (history and proportions): hamradio.in
DX Zone hentenna project index: dxzone.com