Radar Dome vs. Open Array
Every marine radar has to solve the same problem: pack an antenna into something you can actually mount on a boat. A dome hides that antenna inside a spinning weatherproof shell. An open array leaves it exposed as a long rotating bar. The shape you choose changes how sharply your radar can tell two nearby boats apart, how far it can see, and how much hardware you're bolting to your mast — independent of whether the radar underneath is magnetron or solid-state.
Dome-versus-open-array is a different question than magnetron-versus-solid-state — and it's easy to conflate the two, since the antenna shape and the transmitter technology inside it are often shopped for at the same time. In reality they're independent choices: you can buy a magnetron open array, a solid-state dome, a solid-state open array, or (less commonly today) a magnetron dome. This piece is about the antenna housing itself — the physical shape that determines beamwidth, range ceiling, weight, and where on the boat it can realistically live.
The short version, before the details: a dome is a compact, enclosed, low-maintenance antenna that suits the overwhelming majority of recreational boats. An open array is a longer, exposed antenna that trades size and weight for sharper angular resolution and more range headroom. Which one is right depends less on brand and more on what you're asking the radar to resolve.
01 — Fundamentals
Two ways to package the same antenna
Both designs rotate a directional antenna and time the microwave echoes bouncing back. The difference is entirely physical: how long that antenna is, and whether it's enclosed.
A compact antenna, fully enclosed
Inside a dome's fiberglass or plastic housing, a short antenna element — physically limited by the dome's own diameter, typically 19 to 24 inches for recreational units — spins continuously, invisible from outside. The housing protects it from weather, salt, and rigging, and means there's no exposed blade to injure crew or snag a line.
Because the antenna itself is short, its beam spreads wider as it leaves the dome — commonly around 5° of horizontal beamwidth on recreational units. That's the fundamental trade a dome makes: convenience and safety in exchange for angular sharpness.
A long antenna, exposed to the air
An open array is a straight slotted-waveguide bar — no housing, just the antenna itself — mounted on a rotating pedestal. Recreational sizes run 3.5 to 6 feet long; commercial and superyacht arrays extend to 8, 10, even 12+ feet.
That extra physical length is the entire point: a longer antenna focuses its energy into a narrower beam, typically 1.3° to 2.3° depending on length — roughly two to four times sharper than a dome. The cost is size, weight, wind load, and an antenna that lives out in the weather rather than under cover.
Antenna length and beamwidth are directly linked by basic antenna physics — there's no way around it with either technology. A solid-state open array and a magnetron open array of the same physical length will have very similar beamwidths; the transmitter type changes power draw and processing, not the geometry.
02 — Angular resolution
Beamwidth: the number that actually matters
Horizontal beamwidth is the single spec that best predicts how a radar will "feel" to use. A wide beam illuminates a broad wedge of sea with every pulse, so two targets sitting close together in bearing — two boats, a boat near a shoreline, a channel marker against a jetty — can blur into one return. A narrow beam slices that wedge thinner, resolving them as distinct contacts.
Two vessels close together sit inside the same ~5° wedge on a single sweep — the display often merges them into one elongated blob until they separate further.
The same two vessels fall in different narrow slices of a ~1.5° beam — the display keeps them as two separate, clearly bounded contacts.
03 — Range
How far each one sees
Maximum range depends on transmit power and processing more than antenna shape alone, which is why the gap between a well-specced dome and an entry-level open array has narrowed in recent years. Still, the physical ceiling favors the array: more antenna gain, more room for a bigger transmitter, and — on the largest commercial and superyacht installations — antenna lengths recreational boats never carry, which extend range well past what any dome offers.
04 — Size & weight
What you're actually bolting to the boat
The beamwidth advantage doesn't come free. A longer antenna is a heavier, more wind-loaded object spinning above your center of gravity — a real factor for mast strength, arch design, and stability, especially under sail.
That difference cascades into installation. A dome mounts on a simple pole bracket or a sailboat's mast with negligible windage. An open array needs a stronger mount, meaningful clearance to rotate safely over the deck, and enough elevation to clear crew and rigging — which is part of why open arrays are uncommon on boats under roughly 28 feet and rare on anything but the largest, most heavily rigged sailboats.
05 — Head to head
Capability scorecard
A general pattern across recreational-class hardware from major manufacturers. Individual models vary — a large premium dome can out-range a small entry-level array — so treat this as the typical shape of the trade-off, not a spec for any one product.
| Dimension | Dome | Open array |
|---|---|---|
| Target / bearing separation | Wider beam | Advantage |
| Maximum range ceiling | Good, capped lower | Advantage |
| Weight & wind load | Advantage | Significant |
| Ease of installation | Advantage | Needs clearance & strong mount |
| Sailboat / mast mounting | Well suited | Usually impractical |
| Protection from weather & snags | Enclosed | Exposed |
| Typical cost | Lower | ~2x a comparable dome |
| Available as magnetron or solid-state | Both | Both |
| Fit for small/day boats | Advantage | Often impractical <28 ft |
| Fit for offshore/commercial work | Capable | Advantage |
06 — Full spec comparison
Side by side
| Attribute | Dome | Open array |
|---|---|---|
| Housing | Enclosed radome | Exposed, open-air rotation |
| Typical size (recreational) | 19–24 in diameter | 3.5–6 ft antenna length |
| Typical weight | ~14–16 lb | ~42–50 lb (antenna + pedestal) |
| Horizontal beamwidth | ~5.2° typical | ~1.35–2.3°, narrower with length |
| Typical max range | 36–72 nm | Up to 96 nm (recreational) |
| Rotation speed | 24 / 36 / 48 rpm, selectable | 24 / 36 / 48 rpm, some with high-speed tracking boost |
| Wind load | Minimal | Significant — factor into mount/rig design |
| Typical mount | Pole bracket, mast, hardtop | Radar arch, flybridge, elevated open mount |
| Practical minimum boat length | No practical minimum | ~28 ft and up, typically |
| Sailboat suitability | Excellent | Poor for most auxiliary sailboats |
| Relative cost | Baseline | ~2x a similarly powered dome |
07 — Verdict
So which antenna should you actually buy?
This is much more of a "what does your boat need" question than the magnetron/solid-state debate — the right answer is often obvious once you know your typical cruising range and how crowded your usual waters get.
Sailboats & mast-mounted installs
Low windage and light weight matter enormously up a mast under sail. A dome is the practical — often the only realistic — choice for the vast majority of auxiliary sailboats.
Day boats, center consoles, coastal cruisers
For collision avoidance and piloting within a typical 2–20 nm working range, a dome's range and resolution are plenty, and the simple bracket installation keeps cost and complexity down.
Offshore sportfishing & long-range cruising
Narrow-beam resolution helps separate boats, birds, and weather cells at distance in open water, and the extra range headroom pays off well offshore.
Trawlers, motoryachts, commercial & workboats
Boats with the size, power budget, and mounting real estate to spare get real, everyday value from sharper target separation in busy traffic — and it's standard equipment on most commercial hulls for a reason.
The short version: beamwidth is the whole story. A longer, open antenna resolves the world in finer detail and reaches farther, at the cost of size, weight, wind load, mounting complexity, and roughly double the price of a comparable dome. Most recreational boats — and essentially all sailboats — do perfectly well with a dome. Boats that regularly need to pick contacts apart at range, and that already have the size and rigging to carry one, get a genuine functional upgrade from an open array.
Remember the other axis: this choice is separate from magnetron vs. solid-state. Both antenna shapes are available with either transmitter technology, so the two decisions can — and often should — be made independently based on what each is actually solving for.