Dual Frequency PIFA

Well, judging from my fellow students' blogs, SRPs are finally slowing down and beginning to become more focused on presentations and final products. My project is no exception, as I've been rather busy this week trying to plan out my presentation. It's kind of funny, because when I began attending BASIS in 9th grade I was convinced that I was going to graduate early so that I could avoid the 20-minute presentation that was required for Senior Research Projects. Even though in this school year alone I've already given six or seven presentations that long, and presenting doesn't freak me out as much as it used to, it's still pretty surreal to actually be working on my SRP presentation.

Anyhow, this week I went back to the workshop (mostly for fun), and found a PIFA that had an L-shaped cut through the top plane. I was curious, so I decided to make one of my own to see what it does! Here's a picture of the one I made:

My dual frequency PIFA

As many of you are probably guessing because of what it probably my least creative blog-post title to date, this antenna resonates at two distinct frequencies! I painstakingly cut and measured the copper material exactly like I would to make a 1.575 GHz GPS PIFA, but I wasn't too careful with the L-cut that I made. That is to say, I didn't know that it would resonate at two frequencies, so I didn't place special care in the dimensions of the L-shaped cut I made. Take a look at the network analyzer readings I got from my antenna.

Remember that in order to get good transmission at a certain frequency, the network analyzer should have a reading of -10 dB or lower at that frequency, so this antenna resonates well at approximately 1.408 GHz (marker 1) and very well at approximately 2.131 GHz (marker 2). I put marker 3 at exactly 1.575 GHz, because I was curious about what it would look like since the dimensions of the PIFA without the cut would have led to a 1.575 GHz antenna, and interestingly enough there is a little blip at that frequency, but it's only about -4 dB. 

Something that I didn't know until Marcos taught me was that the 2-D area of each part of the dual antenna has a lot to do with the frequencies that they resonate at. I had thought that the piece with the longer perimeter would correspond to the longer wavelength (lower frequency), but it turns out that the piece with the larger area will correspond to the longer wavelength, even if it has a shorter perimeter. 

If PIFAs were to be used in tracking devices for larger animals, where they could be more easily integrated into the circuitry, and there were two frequencies that the device needed to transmit at, then a dual PIFA would be a great option. For instance, if the device had GPS capability, but it also needed to communicate with the receivers in a MURS frequency, one antenna would be able to facilitate both frequencies. That's pretty convenient!

As always, thanks for reading, and have a nice weekend!