Quagi Antenna
The Quagi — a "quad" reflector and driven element followed by lightweight "Yagi"-style director rods — was developed by Wayne Overbeck, N6NB, and published for VHF/UHF weak-signal and satellite work. Quad loops make excellent reflectors and driven elements: self-supporting, reasonably broadband, and a bit more forgiving of construction tolerance than a plain rod. Adding several plain Yagi director rods ahead of the quad pair gets you real gain without the weight and complexity of building an entire boom's worth of quad loops.
Quad loops at the back, Yagi rods up front
The reflector and driven element are both full quad loops — self-supporting square (or diamond) wire loops with roughly one wavelength of perimeter each. Ahead of the driven loop, the boom carries plain straight director rods just like an ordinary Yagi, cut and spaced using the same standard director ratios used in conventional Yagi designs.
Driven loop perimeter: ~1005/f x K (ft)
Director rods: standard Yagi director ratios, progressively shorter forward
Why a quad reflector/driven pair instead of plain rods there too
A quad loop's driven element tends to be somewhat more forgiving of small dimensional errors and gives reasonably wide bandwidth compared to a plain dipole driven element at the same position, while the quad reflector loop provides solid front-to-back performance without needing to be perfectly tuned. Using rod directors for the rest of the array keeps the boom light, since directors don't need to be self-supporting loops the way the driven element benefits from being.
- Quad reflector/driven pair: broader bandwidth, more tolerant of small construction errors.
- Yagi director rods: lighter, simpler, cheaper than adding more full quad loops for the rest of the gain.
Why it's a satellite/weak-signal favorite
The combination gives a strong gain-to-weight and gain-to-boom-length ratio, which matters for anything mounted on a light rotator, elevation-rotator satellite mount, or a portable EME setup. This is exactly the context N6NB originally developed and published the design for.
How many directors to build
More directors add gain but also add boom length and weight, and returns diminish per additional director the way they do on any long-Yagi-style array. Three to six directors is a common practical range for portable and moderate fixed-station Quagis; beyond that, boom sag and mechanical support become real design considerations of their own.
Installation options
- Fixed mast with az/el rotator: the standard setup for satellite work, allowing full tracking of a pass.
- Portable/field mount: a shorter-director-count Quagi mounted on a photo tripod or short push-up mast works well for portable satellite operating.
- Fixed weak-signal/EME station: longer director counts on a well-supported boom suit dedicated weak-signal stations chasing extra gain.
| Element | Length/Perimeter | Notes |
|---|---|---|
| Reflector loop | Perimeter ~85.4 in, each side ~21.3 in | Square quad loop, furthest back on the boom |
| Driven loop | Perimeter ~83.4 in, each side ~20.9 in | Fed loop, spaced ahead of the reflector |
| Reflector-to-driven spacing | ~9.8 in (0.2 lambda) | Typical quad-pair spacing |
| Director 1 | ~36.6 in | First rod director ahead of the driven loop |
| Directors 2-4 | ~2% shorter each, progressively | Standard Yagi director tapering |
| Director spacing | ~16.4 in (0.2 lambda) typical | Adjust slightly per director count for best gain |
Quagi Dimension Calculator
Materials for Quagi
Building the Quagi
Two build phases: the quad loops (reflector and driven) at the back, then the plain rod directors extending forward.
Build the reflector quad loop
Assemble spreader arms into a square, and run wire around the perimeter to the reflector loop's calculated length, closing the loop with no feedpoint break.
Build the driven quad loop
Assemble a second spreader frame and wire loop to the driven element's calculated (slightly shorter) length, this time leaving a feedpoint break at the bottom or side of the loop.
Mount both loops to the boom
Mount the reflector and driven loops to the boom at the calculated spacing, reflector furthest back.
Cut and mount the director rods
Cut each director to its calculated (progressively shorter) length and mount them ahead of the driven loop at the calculated spacing.
Install the feedpoint matching network
Install a gamma match or other matching network at the driven loop's feedpoint break to bring the impedance to 50 ohms.
Connect coax and mount to your mast/rotator
Connect your feedline and mount the assembled boom to your mast or rotator setup.
Sweep SWR and verify the pattern
Sweep the feedpoint for a clean resonant dip, and check gain/front-to-back performance on the air or against a reference station.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR won't come down at the feedpoint | Gamma match (or chosen matching network) not properly adjusted | Check the matching network adjustment first | Adjust the gamma match/matching network — a plain direct coax connection rarely gives a clean 50-ohm match on a quad-loop driven element |
| Gain seems lower than expected for the director count | A director installed out of sequence, or spacing drifted from calculated values | Verify director order and spacing carefully | Correct order and spacing; errors compound more as director count increases |
| Boom sagging over time | Mechanical support issue that worsens with more directors | Check boom material and support against the wind/weight load | Reinforce or upgrade the boom, or add a support truss, rather than accept gradual detuning |
Why quad loops instead of plain dipole elements for the driven/reflector pair?
Quad loops give somewhat wider bandwidth and more tolerance for small construction errors at those two critical positions, while keeping the rest of the array as lightweight rod directors.
How many directors should I build?
Three to six is a common practical range balancing gain against boom weight and mechanical complexity — more directors add gain with diminishing returns and real mechanical tradeoffs.
Do I need a gamma match?
Some form of matching network at the driven loop's feedpoint is standard for this design — a gamma match is the most common choice, though other matching methods can work too.
Is this good for satellite work?
Yes — this is one of the design's classic use cases, thanks to its strong gain-to-weight ratio on a light, trackable boom.
Can I build this for both 2m and 70cm?
Yes, separately — the calculator scales all element dimensions to your chosen design frequency, but you'll build a dedicated antenna per band rather than one dual-band structure.
Who developed the Quagi?
Wayne Overbeck, N6NB, developed and published the design for VHF/UHF weak-signal and satellite use.