Dipole. This is a little more complex sort of antenna, and they’re everywhere. The most common way of thinking about a dipole is a “rabbit ears” antenna but really most indoor antennas, whether they are cats’s whiskers, bowties, loops or flat squares are all dipoles.
What is a dipole?
If you look at a pair of rabbit ears, you’ll see that they look like two monopoles. That’s essentially because they are. However, they’re able to do more than a monopole because of the way a dipole antenna connects to the receiving circuitry. In a monopole antenna, the antenna itself connects to the “signal” part of the cable while the “ground” part of the antenna connects to something else. In a dipole, each of the two elements connects to the cable. This gives the dipole quite a bit more receiving power than the monopole. Both sides of the dipole can be aimed independently although the ideal setup has both sides pointing away from each other.
Types of dipoles
Practically any antenna you see out there boils down to a dipole of some sort. Even fancy yagi and log-periodic antennas are nothing more than variations on the theme.
The basic dipole looks like this:
It’s a pair of elements that extend out and meet a signal on the plane on which it travels. The signal causes the elements to resonate (vibrate with electrical current) in a way that’s consistent with the signal.
The loop dipole
This is the basic form of a loop dipole. It’s a little easier to understand how it’s derived from a basic dipole when you look at this sort of loop dipole:
Here you can see that the loop is really two dipole antennas folded back on each other and connected. This configuration is specifically useful for UHF television frequencies. It’s found in practically any TV antenna.
The bowtie is another form of dipole where the elements are spread at an angle to each other. This makes them more flexible in picking up UHF frequencies.
Oh, and about rabbit ears…
The rabbit ear antenna is a mix of two different dipoles. The “ears” are dipoles which are able to extend and tilt up and down. This makes them sensitive to different frequencies, because an antenna is most sensistive to a frequency that’s an exact multiple of its length. This part is used for VHF frequencies which are fairly low (meaning longer waves) and need adjustments to get all the way from channel 2 to channel 13.
The other part of a rabbit ear antenna is the loop dipole which handles the VHF frequencies.
When should you use a dipole antenna?
Well, pretty much always, at least for TV. The dipole antenna is more effective at picking up specific frequencies and can be combined into a complex array (something for another article) if needed. It’s also the oldest form of antenna, actually having been invented before the monopole. It’s very specific in the way that it’s best used, and the mathematical formulas that govern its use are really, really complex, which is kind of funny when you realize that most of us use dipoles by wildly flailing the elements in weird directions until something looks good.