The Antenna Guy

So, as I mentioned on my last post , here I'll explain about those rings around the feed points on the microstrip antenna. Those rings are copper cutouts around the feed point of the antenna. Those cutouts, at high frequencies, are equivalent to a capacitor. That capacitor is used to compensate the series inductance that is introduced by the higher order modes being driven. Also, the microstrip patch antennas are coaxially fed, the pin of the coax, at high frequencies, acts as an inductor, adding to the increased inductance effect, and the longer this pin wire is, the higher that inductance. That inductance is in series with the antenna and will impact directly on it's input impedance. Here's the variation of the input impedance of the microstrip patch with the variation in height (h) between the patch and the ground plane:   ...

This is a continuation of my previous post on the air core microstrip patch antenna. It can be found  here . At this point, we need to get the patch to radiate a circularly polarized wave (and correct the added inductance of the feed pin by the increased height). Now, if looking at the microstrip patch through the cavity mode analysis, it’s possible to produce two fundamental frequencies of operation, set by the propagation mode that is activated in the patch, these are respectively TM10 and TM01. If the patch is fed along the length, we get the TM10, if it is fed along the width, we get the TM01...or is it the other way around? I always forget which is which! But it doesn’t matter, what is relevant is that we keep in mind that exciting fields in different places of the patch will excite different modes which might have or not the same resonance, but will have a phase delay between them. Feeding on o...

As I mentioned on my previous post, today’s post will be about the good old microstrip patch antenna. There are two implementations for the microstrip patch antenna typically used for UHF RFID ‘Reader’ antennas, one with an air core and other with ceramic core. The advantage of the former is that it has a wider bandwidth (can usually accommodate the ETSI and FCC bands), better efficiency and therefore higher radiation gain and usually has a better polarization purity. The advantage of the later is that it is smaller. That’s it, on ceramic core microstrip antennas, you sacrifice all performance parameters for size. In some applications which are very restraining in terms of available space, it is essential to have the possibility to reach a compromise between the size of the antenna and its performance. Now, as I already mentioned, I’m not going to dwell on the theory of microstrip patch antennas, how they come to be and h...