UHF RFID Antennas - VII - Quadrifilar antenna (Part II)
To continue on the topic of the printed quadrifilar antennas, as promised, this post will be about the feeding network. Last post I've shown the antenna part and a quick explanation as to what the feeding network should look like, this time I'm going to cover the power distribution network that makes it all work. More specifically, I'll explore an alternative that allows the antenna construction to be more compact and with better performance. So the idea is to create a system which has one single input port and four output ports, where all the outputs have the same power and 90º sequential phase difference between them, as explained in the last post. But how exactly does that work and why the antenna becomes circularly polarized, when the single element of the antenna has linear polarization? Well, if you generate two orthogonal electric field components with a 90º phase difference between them, then the