Cubical Quad Antenna: Gain, Build Tips and Yagi Comparison

A cubical quad antenna is a directional wire antenna built from square loops instead of straight rods. It looks unusual next to a classic Yagi, yet it has been a favourite of contest stations and DXers for decades, because a small quad can give a lot of forward gain from a modest boom and a modest tower. This guide explains how a quad works, how it compares with a Yagi, what to think about before you build one, and why many operators who love their quads also admit that they are a lot of work to maintain.

The aim is not to sell you a quad. It is to help you decide whether the loop approach fits your site, your tower and your patience. If you are still choosing between beam designs, the comparison in our guide to the Yagi and hex beam is a good companion read.

What a Cubical Quad Actually Is

A quad is, in effect, a Yagi-Uda antenna made from loops. As the overview of the quad antenna puts it, it consists of a driven element and one or more parasitic elements, but each element is a closed loop that may be square, round or some other shape. The “cubical” name comes from the most common building style, in which each loop is a square supported at its corners by a cross of spreader arms, so that the whole element looks like a cube seen from the front.

The driven loop is about one wavelength around. The parasitic elements work exactly as they do on a Yagi: a reflector slightly larger than the driven loop sits behind it, and directors slightly smaller sit in front. Because the loops are closed, there are no open ends, which matters in two ways. There is no end effect, and there is less tendency for the high voltages at the tips of a dipole element to cause corona discharge in thin air.

That second point is where the design came from. The quad is generally credited to Clarence Moore, an engineer at the missionary station HCJB high in the Andes, who patented a loop antenna in 1951 to avoid the corona problems he saw with conventional beams at altitude. The multiband cubical form that amateurs build today followed a few years later, and several variants, such as the Swiss quad and the DJ4VM quad, appeared in the following decades.

How the Quad Compares With a Yagi

Quad enthusiasts often claim a long list of advantages. Some are real, some are folklore. The table below separates the two as honestly as possible, based on published measurements and modelling rather than on anecdotes.

The gain figure in the table is the often-quoted one: a two-element quad has about the gain of a three-element Yagi, roughly 7.5 dB over a dipole, and a three-element quad outperforms a three-element Yagi. Returns diminish quickly as you add elements. Authors of the classic quad books concluded that the practical limit for a parasitic loop array is about four or five elements, which is a very different world from the long-boom Yagis used on the low bands.

The one claim that does not hold up is that quads “open the band earlier” because they have a lower radiation angle. Computer modelling shows no such difference between a quad and a Yagi mounted at the same height. If your quad seems to hear more at the start of an opening, the cause is more likely its height, its location or simple luck. The effect of height on take-off angle is covered in our article on antenna height and take-off angle.

Polarization and the Feed Point

One of the most practical features of a quad is that you can choose the polarization by deciding where to attach the feed line. If you feed the loop at the middle of a horizontal side, the antenna radiates a horizontally polarized signal. If you feed it at the middle of a vertical side, the antenna radiates a vertically polarized signal. No other change to the structure is needed.

For HF work, horizontal polarization is the usual choice, because a horizontally polarized beam at a good height gives clean patterns and avoids some of the ground losses of a vertical. For VHF and UHF, quad designs are used with either polarization, depending on the mode you operate. Some builders feed one corner of the loop for a mix of both polarizations, a method that is sometimes used on quads for satellite work, though the details are beyond this guide.

Because the radiation resistance of a quad is higher than that of a Yagi and closer to the 50 ohm coax most stations use, the match is often easy. A common solution is a quarter-wave section of 75 ohm cable as a transformer, or a choke balun at the feed point, because the loop is a balanced antenna and a coax feed line is unbalanced. Our article on baluns and ununs explains the choices and why a good choke at the feed point pays off for any balanced antenna.

Single-Band and Multiband Quads

A single-band quad is the simplest version: a square driven loop, a reflector and, if you want more gain, one or more directors, on a boom of modest length. Even a two-element quad on 20 meters is a sizeable object, because the loop is about a wavelength around and each side is a little over a quarter wavelength. A quad for 10 or 15 meters is small enough for a light tower and a modest rotator; one for 40 meters is a major structure.

The multiband quad is where the design really shines. Interaction between loops tuned for different bands is low, so higher-frequency loops can be nested inside lower-frequency loops on the same spreaders, with each band having its own driven element and reflector. This can be fed by a single coax line, or by separate lines to each band. For a station with room for only one antenna, a two-element three-band quad can be a very effective choice.

• Single-band quads are the easiest to build and tune, and best when you operate mostly on one band, for example on 10 meters in a solar maximum.
• Dual-band and tri-band quads add complexity, but share spreaders and boom, and give you three bands from one rotator.
• Quads for VHF and UHF are lightweight and small, and are a good first project for someone who wants to learn how loops behave.

Design Choices That Matter

Loop shape

Square loops are the standard because they are easy to support with spreaders, but diamond (corner-up) and round loops are also used. A diamond mount puts the feed point at the bottom corner for horizontal polarization, and uses a single vertical support. A round loop is slightly more efficient for its wire length, but is harder to build and support. The shape changes the effective dimensions only slightly, and the antenna is tuned by trimming in any case.

Element spacing

Typical spacing for a two-element quad is around a tenth to a fifth of a wavelength. Narrower spacing makes the antenna more compact, but also narrows its bandwidth and lowers the feed impedance. Wider spacing gives a bit more gain and a wider bandwidth, but costs boom length. Published designs give good starting points, and the ARRL antenna resources point to the standard references. Use a trusted design rather than inventing one, then tune it on the day.

Bandwidth

If a three-element quad is tuned for maximum gain, its bandwidth is limited, because moving off the design frequency unbalances the near-resonance of the parasitic elements. Lengthening the directors costs about 1 dB of gain but gives a much broader bandwidth. On wide bands, such as 10 meters, many builders accept that trade, while on narrow bands they favour maximum gain.

Building a Quad That Lasts

The quad’s weak point is mechanical. A quad is a three-dimensional antenna, with wire, spreader arms, joints and guy lines, all exposed to wind, rain, ice and sun. A quad that looks wonderful on day one can droop, sag and drift out of tune within a couple of seasons if it is not built with care. These are the lessons that experienced builders repeat.

1. Choose spreaders for strength and weather resistance. Fibreglass spreaders are the usual choice. Bamboo is cheap but needs treatment and eventually fails.
2. Use proper antenna wire. Stranded copper-clad or hard-drawn wire with a stable jacket resists stretch better than soft wire, and the loop dimensions stay closer to the design.
3. Insulate the joints and seal the feed point. Moisture in the feed point changes the match and corrodes connections.
4. Support the wire against sag. Use light nylon or polyester cord to keep the loops taut without putting load on the wire itself.
5. Plan for lowering the antenna. A quad is much easier to maintain if it can be tilted or lowered to the ground, rather than serviced with ladders or a bucket truck.
6. Add a choke at the feed point. A balun or choke prevents the coax from becoming part of the antenna and distorting the pattern.

Before the first transmission, plan to measure the antenna with an analyzer. A tool such as a NanoVNA lets you sweep the whole band and see exactly where the antenna is resonant. Our NanoVNA guide explains how to calibrate and sweep, and the same steps apply when you trim a quad element by element.

Tuning and First Tests

Tuning a quad takes patience, but follows a simple order. First, set the reflector and any directors to the lengths in the design, and measure the driven loop. Then trim the driven loop in small steps until the lowest SWR falls where you want it. When you adjust the reflector, you change the pattern and the match together, so work in small steps and keep notes.

• Test at the height you intend to use, or as close to it as possible. A quad on the ground behaves differently from one on a tower.
• Keep metal objects, including the mast and rotator, in mind. They detune the nearest elements.
• Check for pattern, not just SWR. A good match alone does not tell you whether the antenna has a clean front-to-back ratio. Use another local station, or a reverse beacon, to compare directions.
• Record your final settings and photograph the antenna. When a storm shifts something, you will be glad to have the reference.

If you plan to turn the quad, think about the rotator early. A quad has a large wind area on its loops, so the rotator and the mast must handle both the torque and the weight. Our antenna rotator guide shows how to size one.

Quad Alternatives to Consider

If you like the idea of a loop-based beam but not the maintenance, there are related designs. A Moxon rectangle, covered in our Moxon antenna guide, is a compact two-element wire beam with a good front-to-back ratio. A hex beam, mentioned above, is a lighter wire beam with a larger multiband span. A conventional Yagi is stronger in a storm. Each design trades gain, bandwidth, weight, wind load and cost differently, and the best choice depends on your tower, your neighbours and the bands you use most.

Common Mistakes to Avoid

• Building from a vague design. A quad is sensitive to spacing and element length. Use a trusted published design and follow it.
• Ignoring the weight. Wire, spreaders and boom add up. Check the load rating of the tower, mast and rotator before you buy materials.
• Skipping the choke. Without it, the coax radiates and the pattern suffers.
• Expecting a magic low angle. A quad does not reach lower than a Yagi at the same height. Put your effort into getting it up high.
• Underestimating maintenance. Plan an annual inspection with a way to lower or tilt the antenna safely.

The Bottom Line

A cubical quad antenna is a loop-based Yagi that delivers strong gain from a short boom, offers a convenient feed-point polarization choice and can be nested for several bands. It is not magical: it has no lower take-off angle than a Yagi, and it needs more care to keep in good condition. If you have a sturdy tower, a rotator that can handle the wind load and a plan for maintenance, a well-built quad can be one of the most rewarding antennas on the roof. If not, a Moxon, a hex beam or a rigid Yagi may serve you better. Start from a proven design, measure with an analyzer, and build for the weather you really have.

Frequently Asked Questions

How much gain does a cubical quad antenna have?

A two-element quad has roughly the same gain as a three-element Yagi, about 7.5 dB over a dipole according to published comparisons. A three-element quad has more gain than a three-element Yagi, but adding further elements gives diminishing returns.

Is a quad better than a Yagi?

It depends on what you value. A quad gives more gain on a shorter boom and is easy to make multiband, but it is heavier on maintenance and more exposed to wind and ice. A Yagi is more rigid and simpler to keep up.

Does a quad have a lower take-off angle than a Yagi?

No. The idea that quads open the band earlier has been persistent, but computer modelling does not show a lower radiation angle for a quad compared with a Yagi at the same height.

How do I change a quad from horizontal to vertical polarization?

Move the feed point. Feeding the middle of a horizontal side gives horizontal polarization, and feeding the middle of a vertical side gives vertical polarization. The rest of the antenna stays the same.

Can one quad cover several bands?

Yes. Because the interaction between loops of different sizes is low, smaller loops for higher bands can be nested inside larger loops on the same spreaders, with each band having its own driven element and reflector.

What is the biggest drawback of a quad?

Maintenance. It is a three-dimensional wire structure exposed to weather, and servicing it usually requires lowering the antenna or climbing. Planning for tilt-over or lowering from the start makes a big difference.