Hentenna
The Hentenna is a folded wire loop, roughly a wavelength of wire bent into a tall, narrow rectangle, that matches directly to 50-ohm coax with no balun, no gamma match, and no external matching network at all — you tune it by sliding the feedpoint tap along the bottom wire instead. That single trick is the whole reason to build one: it's a genuinely simple, lightweight VHF antenna for portable and satellite work that performs close to a dipole, sometimes a bit better broadside, without adding a matching component to fail or misplace in the field.
Two vertical radiators joined into one loop
Picture two half-wave vertical elements standing side by side, spaced roughly a quarter wavelength apart, with their top ends joined by a short wire and their bottom ends joined by another short wire — that closed rectangle is the Hentenna. Because the two verticals are connected into a single loop rather than fed separately, the loop's own current distribution keeps them running in phase with each other without a separate phasing harness, which is what gives the design its mild gain over a plain dipole.
Side-to-side spacing: ~0.25-0.3 wavelength
Loop closure keeps both verticals in phase -- no phasing line needed
Why the feed tap replaces a matching network
Current and impedance vary continuously along the bottom connecting wire of the loop, from a low-impedance point to a much higher one. Sliding the coax feedpoint along that bottom wire lets you find the exact spot where the loop presents close to 50 ohms directly — the same principle a gamma match uses with an external rod, except here the loop's own geometry does the matching, so there's no separate matching component to build, weatherproof, or lose.
Performance expectations — dipole-class, not a beam
Don't expect Yagi-style gain from this design. Independent modeling and long field use both put the Hentenna's forward gain in roughly the same range as a plain half-wave dipole, with a modest edge (commonly cited around 1-2 dBd) broadside to the loop from the two-in-phase-element effect. Its real advantage is mechanical simplicity, not raw performance.
Where the design and its name come from
Unlike the Moxon or Quagi, the Hentenna doesn't trace back to one clearly documented published paper — it circulated through Japanese amateur radio circles under a name that translates roughly to "strange antenna," and spread internationally through VHF/UHF portable and satellite operating communities rather than a single named inventor's article. Treat the exact provenance as folk-design history rather than a citable formal reference, the same honest caveat that applies to a few other well-loved but informally-documented designs.
Installation options
- Handheld/portable mount: light enough to hand-hold on a short mast or hang from a strap for SOTA/POTA or satellite work.
- Fixed mast, vertical polarization: mounted with the loop's long axis vertical for FM/repeater work matching typical VHF vertical polarization.
- Fixed mast, horizontal polarization: rotated 90 degrees for SSB/CW weak-signal work where horizontal polarization is conventional.
| Parameter | 2m (146 MHz) | Notes |
|---|---|---|
| Each vertical side | ~40.5 in (1.03 m) | ~0.5 wavelength; the two radiating elements of the loop |
| Side-to-side spacing (top/bottom wire) | ~20.2 in (51.3 cm) | ~0.25 wavelength; connects the tops and bottoms into a loop |
| Total wire, full loop | ~10.1 ft (3.1 m) | Cut a few inches long on all sides and trim to resonance |
| Feed tap position | Found empirically | Start near the loop's bottom-center and slide toward one vertical side while watching SWR |
Hentenna Dimension Calculator
Materials for Hentenna
Building the Hentenna
The frame and loop are simple; finding the feed tap point with an analyzer is the one step that takes real patience.
Build the non-conductive frame
Assemble a fiberglass or PVC frame to hold the loop's rectangular shape, sized to the calculator's vertical and horizontal dimensions.
Form the loop conductor
Bend or mount rod, wire, or tubing around the frame to form the closed rectangular loop, cutting a few inches long on the total perimeter for trimming later.
Install a movable feedpoint clamp on the bottom wire
Mount the coax center conductor and shield to a clamp or slider that can move along the bottom horizontal wire without needing to be re-soldered each time you test a new position.
Mount the loop to your mast or handle
Attach the frame to a mast, tripod, or handle grip, orienting the loop's long axis for your intended polarization.
Sweep SWR at the starting tap position
Connect your analyzer at the initial feed tap (near bottom-center) and note the SWR and resonant frequency.
Slide the tap and re-sweep until SWR is lowest
Move the feed tap a small distance toward one vertical side, re-sweep, and repeat — impedance changes continuously along the bottom wire, so small moves make a real difference.
Trim the loop to final resonance
Once the tap position gives a good match, trim the loop's total perimeter evenly to bring the resonant dip to your exact target frequency, then permanently solder the feedpoint.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Can't find a low-SWR tap position anywhere on the bottom wire | Loop dimensions are significantly off from resonance | Check overall loop perimeter and side lengths against the calculator | Correct the loop dimensions first, then resume the tap search |
| SWR is good but shifts every time the antenna is handled | Feed tap connection isn't mechanically solid | Check for a temporary clip connection instead of a soldered joint | Solder the final feedpoint once the tap position is confirmed |
| Performance seems no better than a plain dipole | Expecting beam-like gain from a design that doesn't provide it | Compare against the design's realistic 0-2 dBd expectation | Not a fault — this design's advantage is simplicity, not gain over a dipole |
Do I really not need a balun or matching network?
Correct — the whole point of sliding the feed tap is to find the point on the loop that already presents close to 50 ohms, without an external matching component. A common-mode choke at the feedpoint is still a reasonable addition, but it's optional, not required for the match itself.
Is this a gain antenna?
Only modestly. Expect dipole-class performance with perhaps 1-2 dBd of broadside gain from the two-in-phase-element effect, not Yagi-class directional gain.
How precise do the dimensions need to be?
Less precise than you'd think — because the feed tap position does most of the real matching work, small errors in the loop's overall size mostly shift the tap point rather than preventing a match entirely. Still start from the calculator's values rather than guessing.
Can I build this for HF instead of VHF?
Yes, the same geometry scales to any band, though the loop becomes large at low HF frequencies — most builders use this design at VHF/UHF specifically because the size stays manageable there.
Which polarization should I use?
Mount the loop's long axis vertical for FM/repeater work, or horizontal for SSB/CW weak-signal and satellite work where horizontal or circular polarization is more common.
Why is it called a "strange" antenna?
The name comes from Japanese amateur radio circles and translates roughly to "strange" or "weird" antenna — likely a nod to how unusual it seemed to match 50 ohms directly with no external network, using just a sliding tap point.