How can antennas be shaped like Xs and Os?

It isn’t tic-tac-toe, you know.

Take a look at the antenna at the top of this article.  It’s the Antennas Direct Clearstream 2V. The elements are nice and round. Now take a look at this antenna, the Xtreme Signal HDB2X:

 

 

It looks pretty similar, but the elements are shaped like the letter “X.”

Your average person would say that it has to be one or the other. One of these designs has to be inherently better than the other. Your average person would be wrong.

Both designs are different ways of getting to the same place. The X-shaped antenna is more commonly referred to as a “bowtie.” Antenna enthusiasts would call it a “dipole.” A dipole is essentially a piece of wire folded in half with the two halves at differing angles to each other. If you think that simple explanation applies to pretty much every antenna you’ve ever seen, you’d be right.

The O-shaped antenna is more properly called a “folded dipole” or “loop dipole.” One theoretical advantage of the loop dipole is that it functions as a standard dipole of the same size, and also as a dipole of double its size.

Back to basics

The most basic thing you need to know about any antenna is that it does its best work when it’s the same size as the wave it’s trying to receive. For example broadcast channel 30 has a wavelength of about 18 inches. The perfect antenna to get broadcast channel 30 would be 18 inches long. The next best thing would be an even fraction of that, like 9 inches or 4.5 inches. This simple fact accounts for a lot of the differences in the shape of antennas. VHF channels (those below channel 14) have much longer wavelengths, so antennas need to be a lot bigger in order to be efficient. Higher numbered channels have much shorter wavelengths, and really high frequencies like those used for satellite have very very short wavelengths. That’s why the actual antenna part of a satellite dish can be smaller than a dime and still work well.

Keep it simple, stupid

When you research the difference between folded dipoles and standard dipoles, or as we call them O’s and X’s, you run into a huge amount of math and theory. All of that is extremely important if you’re designing an antenna. Really it is.

I know that some folks out there are going to lambast me in the comments for this, but all that math doesn’t do a lot of good in the real world. Why? Because the world is a random place. Of course what you do is put the best-designed antenna in place for the situation and hope for the best. There are so many factors that come into play in the real world that you can’t do much more. There can be obstructions that aren’t obvious, thermal pockets that can warp a signal, reflections from buildings and hills, all sorts of things.

Which really performs better?

In this article, our own Phil Karras tested a loop antenna vs. a bowtie antenna of similar size. He found that on average, the double-loop antenna performed better than a single bowtie. That’s to be expected. Other tests I’ve read on the internet suggest that a double loop antenna and a double bowtie antenna (in other words, the two antennas I’ve pictured above) perform very similarly. The second bowtie makes up for the difference very well. There is a theoretical benefit to the loop antennas but in the real world it’s within the margin of error.

Based on the math, I would guess that a loop antenna would do better at picking up frequencies it’s not supposed to pick up, like those much longer wavelengths found on VHF channels. But, I’m not sure that’s super important, unless you accidentally buy the wrong antenna. In the case of the antenna at the top of this article it also has a VHF dipole (the bar at the top) so that part handles VHF, the loop parts don’t.

When it comes to these two antennas, it isn’t about the shape of the elements. The Antennas Direct model has a VHF attachment, and if you need that, you should choose that antenna. It also comes with a free mount, but overall it’s more expensive. The Xtreme Signal antenna isn’t as good for UHF but it’s less expensive overall and is a great choice if you already have a mount (like if you are replacing an antenna or taking down a satellite dish.) That’s what this is really all about. Don’t get hung up on the X’s and O’s. That’s not the really critical thing here. It’s all the other stuff that really makes a difference.