PIFAs are Everywhere!

Hello again, and welcome back to my SRP blog! I have to say, it's really enjoyable to work in a university lab. As I've already mentioned, there are a lot of neat tools around, and there is an absurd amount of books about antennas. So if you have any questions about antennas, I can get back to you in a couple of business days with an answer (most likely). Also, the lab is the one place I know where my work habits are safe from my recent and extensive obsession with Parks and Recreation. Oops.

For the last week or so I have been working on building my own antennas. It was a ton of fun, even if it took me a couple of days to properly solder anything, and it took a whole day to tweak them after they were built. The type of antenna I was working with is called a PIFA antenna, and below is a picture of the two that I built. They don't look fantastically different from the model PIFA that I took a picture of last week, but that's a good thing I suppose.

My two 1.575 GHz PIFAs

This may be a gross oversimplification of antennas, but the reason why antennas are so helpful for us with modern technology is that they allow different devices to communicate with each other and transmit data, so long as the components that are communicating with each other are operating at the same frequency. The physical properties and dimensions of each antenna determine what frequency the antenna will operate at. Take a look at the data that the network analyzer took from one of the PIFAs that I built.

The peak resonance for this PIFA is practically exactly 1.575 GHz

The horizontal axis of this graph is a range of frequencies that the antenna is tested for, and the vertical axis is the return loss of the antenna. The lower, or more negative, the return loss is, the better the antenna is able to pick up and transmit signals at a certain frequency. The return loss is in decibels, which is 10*log( [% of signal returned] / [% of original signal] ). Therefore, according to this graph, less than 1% of the original signal at 1.575 GHz is returned, and more than 99% is transmitted. This is great! Ideally, this graph would just be a flat line at zero across all frequencies and an infinitely negative value at 1.575 GHz, but, alas, my PIFA-making skills are not that great yet. Just kidding, that would be impossible because there will always be human error and noise.
For those really interested in the workings of the PIFA, the length of the top plane plus the length of the distance between the two plates is supposed to be equal two a quarter-wavelength of the radiowave, but the antenna will also pick up the frequency that corresponds to a half-wavelength of another radiowave, which is why there is another return loss peak at about 3 GHz.

This tidbit probably relates to more of you out there: PIFAs are actually in use in many smartphones! Obviously they don't look too much like the clunky things that I've been making out of copper, but they are there, and oftentimes the ground plane (the larger of the two planes) is actually the back of the phone, and the top plate is concealed inside the phones and integrated very efficiently with the help of remarkable electronics packaging. If you don't believe me, check out the picture below of a Samsung Galaxy S. The six individual plates on the diagram on the right each serve as the top plate for a PIFA at different frequencies, and they all share the same ground plate. If you're anything like me, you've always wondered how the heck smartphones don't have antennas sticking out of them, and this is pretty fascinating and exciting.

Samsung Galaxy S and its fabulous PIFAs

I'll stop raving about antennas for now. Now that my PIFA mission has been completed, I will be reading all about the last three years of Golden Lion Tamarin collar research in order to get a 30,000 feet view of the entire problem so that I can start researching solutions and applications for otters. Plus, I have an entire 200-page book about otters, which I'm very excited to read. Because otters are adorable. I promise I'll find good pictures of otters for the next blog post, because frankly I don't think the otters would feel comfortable among a bunch of technology pictures. Until next week!

Source: http://www.antenna-theory.com/antennas/patches/samsungantennas.jpg