What is beam width?

You know what I hate about antennas? See, most people don’t want to do a ton of math and look at goofy polar charts to understand how to point an antenna. If you’re someone who does, that’s great, don’t get me wrong. But most people don’t.

So you hear this term a lot, “beam width.” These are two fairly small, common words and it should be easy to understand, but then when you google it, you get something like this from Wikipedia:

In a radio antenna pattern, the half power beam width is the angle between the half-power (-3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe.

Uh, yeah.

I mean, all that is important, but what you really want to know is can you get channel 5, and that doesn’t seem to be part of that definition.

The scientific definition of “beam width” is important, but here’s one that makes a little more sense. “Beam width” is a measure of how far off aim you can be when you are pointing an antenna. That’s all, really.

Like, if you’re aiming your antenna and you want to get channel 5, which is at 230 degrees, and you have an antenna with a beam width of 45 degrees, you can aim it anywhere between 207.5 degrees and 252.5 degrees and still get some signal. Let me back up and explain how I got there.

If the beam width is 45 degrees, that means you can aim 22.5 degrees to the left of where you should, or 22.5 degrees to the right. Because, 22.5 is half of 45. Your beam width always goes halfway to the left, halfway to the right. The strongest beam is when you are aiming straight on where you should.

Why do you care? Unless all your stations come from one place (New York City folks, I’m talking to you) aiming an antenna is going to take some compromise. Some stations will be off-aim a little bit, and the goal is to find a place to aim the antenna where you can get all your stations.

An antenna with a wider beam width (in other words, a bigger number) lets you aim even further off of where you would need to. One with a narrower beam width (a smaller number) is harder to aim but usually is more sensitive in that small area.

Generally you would use an omnidirectional antenna (one that pulls in signals from all directions) if you were very close to broadcast signals (under 20 miles), then one with a medium beam width for 30-50 miles, and if your stations were 50 miles or more away, you’d be ok with a narrow beam width because you’d get more of those distant signals.

I hope that explains things a little better for the non-engineers in the crowd, and I hope that the engineers who read this will understand that I had to simplify things a little bit to help make things easier to understand.