Radar: Do You Really Need Open Array?

When it comes to radar systems, the most common question I hear is “do I need an open array?” And there’s a lot of misinformation out there, about this topic. Let me try to put one thing in a nutshell, right off the bat: merely choosing between open array versus dome is no choice at all, because neither is inherently better, nor worse. The reason many people think open array is better is because most manufacturers make open arrays for their higher-end units. Are they better than the same manufacturer’s less expensive dome units? Sure. But it has nothing to do with whether or not the antenna is enclosed in a dome.

The more important factors to look for are beam width, and power. Beam width has a significant effect on sensitivity, as radar pulses may be broadcast at anywhere between about six degrees and one degree. The narrower beam width is, the more focused the radar’s pulses are. This translates into better differentiation between targets. For most anglers, this is important because of the ability to spot birds from miles away.  Generally speaking, the larger, more powerful your radar is, the narrower beam width is likely to be. But there’s a down-side to consider, too; very narrow beam width can limit close-quarters radar visibility, because minimum target width is dictated by minimum beam width. Power, on the other hand, will determine how far out into the distance your radar can see. Relatively weak radars usually have around two kilowatts of power, mid-range units have between four and 12 kilowatts, and the strongest may put out as much as 25 kilowatts. Some of these can see as far as 72 miles away. Or, at least they have that ability—in the real world, it’s a different story.

The single most important factor in determining how far any radar unit will be able to see out into the distance is the height of its antenna. Here’s where many boaters over-spend. Radar range is limited by the curvature of the Earth, and the height of your radar antenna and the height of the target you’re looking at will determine whether or not your radar can see over that curve. Here’s the key formula to remember: 1.22 nautical miles x square root height of radar + 1.2 nautical miles x square root height of target. No matter how powerful your radar is, no matter how tight the beam width, and regardless as to whether it has an open array or a dome, this mathematical calculation will limit your radar’s range. Period.

Again, if you live in the real world, this fact means that unless you own a 50 or 60 footer with a giant tuna tower, purchasing a high-dollar, long-range radar is probably a big waste of money. And whether the antenna is a dome or an open array is, in most cases, completely irrelevant.

radar

Even though the open array radar on this boat has a range of over 40 miles, due to its height, the “real” range is less than half of that.

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