Whips, Zig-Zags, and More Weird Names for Antennas

Hello again! As promised, this post will be about what I've learned about antennas. I've been trudging my way through the first part of what I've heard is the essential book on antennas, eponymously named Antennas, by John Kraus. When I told Mr. Balanda that I wanted to do an engineering SRP, he warned me that engineers don't really learn things. He said that engineers learn how to learn and find information, and know I think I actually understand what he meant. The antenna book has hundreds of different equations relating to antennas, and I'm pretty sure I would cry (manly tears) if I had to learn everything in that book. That being said, going through the book is rather fun, because it involves a lot of step-by-step math and physics, and I even got to use some double integrals to solve some particularly cool problems.

From what I've gathered, the considerations for antennas most relevant to my project (and really almost any project involving antennas) is the size and the directivity of an antenna. Given a specific frequency, different types of antennas will be different sizes, so an appropriate antenna can be chosen based on specific considerations and conditions. For example, the proposed tracking devices will transmit in the MURS (multi-use radio system) band, which ranges from approximately 151-155 MHz. Let's consider the size of three different antennas that could be used for a small mammal tracking device: PIFAs, monopole antennas, and zig-zag antennas.

Hurray for computer programs!

Remember my 1.575 GHz PIFA? Well, I finally get to brag about it again. After I tried to make my HFSS model more accurate by giving it a stem, turning the planes into rectangular prisms, and adding dielectric where necessary, but the program claimed that its peak resonance is at 1.590 GHz. Close enough for government work, I suppose. Unfortunately, a PIFA in the MURS band, which is about one-tenth the frequency of my PIFA, would have to be ten times the size, meaning that the ground plate alone would be 30 cm wide! Even without the stem (which is a valid option), this is not a realistic antenna for a small mammal to have, especially with how fragile a PIFA can be.


Everybody recognizes a monopole antenna, which is essentially just a wire with a length equal to a quarter-wavelength of the frequency it is transmitting at. It can be as simple as a car radio antenna. Similar to a PIFA, a monopole antenna with its peak resonance in the MURS band will have a length of approximately 50 cm, but will be much lighter and more compact than a PIFA at the same frequency, and will fit on animals more easily. Known commonly as whips, monopole antennas are already commonly used on animal trackers, and usually interfere very little with an animal's regular activities.

A Golden Lion Tamarin with a Holohil RI-2D Transmitter

Unfortunately, the whip antenna does not work perfectly for every animal. Some animals, especially like the Golden Lion Tamarin pictured above, live in an environment where long and protruding antennas can easily get caught on things like branches, and a Senior Design Team of Dr. Melde's from 2013 came up with what I think is a brilliant new antenna to solve this problem. Pictured below is what they call the zig-zag antenna. It is very space-efficient because not only is it a mere 20 cm long, but it also can be easily integrated into a wearable collar, as suggested by the fact that the antenna in the picture below is sewn into a cloth.

A zig-zag antenna that does the same job as the other antennas, but it's smaller!

As I mentioned earlier, directivity is another important consideration when deciding on which type of antenna to use. What is directivity? It's one of those slightly annoying unit-less physical properties that doesn't mean anything by itself, but is useful when comparing them to those of other antennas. Basically, the more directive an antenna is, the more direct the beam of radiation the antenna puts out. Here's a wonderfully convenient picture that I'll use to explain:

These polar diagrams show how strong the radiation or the signal is from an antenna depending on what angle you are at around the antenna. The farther away the polar curve is from the origin at a particular angle, the stronger the signal from the antenna is at that angle. As the diagram shows, whip antennas are basically omnidirectional, and thus ideal for animal tracking because you want to use an antenna that will give you a signal no matter how the animal is oriented. Examples of more directive antennas are on the right, and the Yagi-Uda array is an antenna of particular interest to this project, but I'll talk more about that next week when I discuss tracking systems.

Speaking of tracking systems, my project is getting pretty interesting now that I know enough background information about antennas, devices, and otters to research tracking systems in a wider sense. After I read about existing systems that work and this sweet new book specifically about how electronic tracking devices work in water environments, hopefully in a few weeks I'll have a couple viable tracking systems for otters that I will be able to talk intelligently about. I'm excited about next week's blog post, because I'll get to blabber on about the difference between triangulation, GPS, and cell multilateration.

Hasta luego! As always, I'd love to hear any questions!

P.S. I've been listening to a ton of music (as usual) and I just found this awesome band called Ava Luna that reminds me of both Broken Social Scene and Dirty Projectors at the same time, and you can't go wrong with that. If you haven't heard of any of those bands, you're missing out!

Sources: 

Kraus, John, Antennas (McGraw-Hill Book Company, Inc., New York, 1950).

Pictures: 

http://www.holohil.com/GLTamarin.jpg

http://www.cdt21.com/parts/zu/zu_11.gif