How can an antenna work when it’s mostly empty space?

The same way a fish net catches fish. Look at that antenna up there. There’s a lot of empty space in it, and that might get you a little incensed considering that you have to pay for it. Before you really get riled, though, keep in mind that the antenna would be a lot more expensive if it were solid aluminum from top to bottom, and it would be heavier and tip over in a stiff breeze.

Truth is you don’t need any more metal to get a really good signal. This is going to be a bit of a simplification (and the real heavy RF guys are going to feel inclined to correct me) so here goes…

Radio waves come in all different “sizes.” The size of a wave is called its wavelength. When a radio wave hits a piece of metal, it transfers some of its energy to the metal. (Again don’t rip me apart, this is just a vastly simplified way of describing what’s going on.) There are three really critical parts of the process that you need to know:

  1. The metal starts carrying an electrical signal that matches the radio wave’s characteristics exactly. That’s how you can actually get pictures and sound from radio waves.
  2. Different size pieces of metal do a better job with different size frequencies.
  3. You can block frequencies by making a metal cage and it works just as well as if it were solid metal (there’s a “but…”)

So what you have with an antenna are some pieces of metal (we’ll call those “elements”) that are just the right size to pick up some radio waves, and some pieces of metal (we’ll call those “reflectors” that block those waves and send them back, so that same element can pick up even more radio waves.

Getting back to the first line of the article, the key is to space those “reflectors” out just enough so air can pass through them but radio waves can’t. Remember I said there was a “but?” That’s it. You need to space those reflectors out just right so they block the very frequencies you want. Too far away and those radio waves will pass right through, like a little fish passes through a big net.

So bottom line here is, when you’re looking at an antenna, this is the result of a lot of science designed to give you the least possible amount of aluminum (to save weight and cost and reduce wind resistance) and still give you the best possible result. It’s pretty cool all the steps it takes to design an antenna, and at the end of the day you get something amazingly effective, when you realize you’re looking at an HD signal from up to 70 miles away.