This is an antenna. Maybe it’s like no antenna you’ve ever seen, but it’s still an antenna. You’ve probably noticed that antennas come in many different shapes depending on the job requirements. How can that be?
You’ve seen monopole antennas on radios and portable TVs, as well as older cell phones. They’re not very good, but they don’t take up a lot of space. The monopole antenna is pretty much limited to small electronics, so they’re not interesting to home theater folks.
The most common antenna, though, is the dipole. The dipole antenna is a pair of wires that’s set so the entire length of the antenna is visible when pointed at the tower. The antenna you see above is a yagi antenna, which is really just a series of dipoles placed at specific distances so they don’t interfere with each other.
The antenna at the top of the article is a dipole, too: It’s a special type called a loop dipole. Loop dipoles do an excellent job of picking up UHF signals. So do “bowtie” antennas like this one:
You’re thinking, “that doesn’t look like a pair of wires!” There’s a little more to this type of antenna, but at its heart it’s still a humble dipole. The antenna part is really just the X-shaped elements at the front. UHF antennas perform best when shaped like an X, because they do a better job of picking up more of the signal when the elements aren’t at right angles to each other.
The other part, the bars that go across… that’s called a reflector. When you point an antenna at the towers, the signal hits the front part of the antenna. If you use a reflector, it bounces the signal so that it also hits the back part of the antenna. This makes the antenna much more efficient. The reflector doesn’t need to be solid to work, and giving plenty of room for air to pass through makes the antenna more weather resistant.
And then there’s…
This is an antenna, too. Just like in the UHF antenna, the actual antenna part is in the front, and a reflector concentrates all the signal into one spot. Dish antennas have a parabolic reflector which does a better job of focusing the signal into the tiny antennas in the front, and complicated electronics isolate the signal from the noise around it.
An antenna’s design really depends on what it is supposed to pick up. Large Yagi antennas are most effective at picking up VHF signals, while the bowtie and loop designs really excel at UHF. Dish antennas are best for picking up satellite frequencies that are much, much higher than “terrestrial” broadcast. So you see, it’s all about what kind of signal you want to capture.