If I have two circular polarized antennas on each side of a door, should one be left-polarized and the other right-polarized?
Good question. I assume you are talking about a passive ultrahigh-frequency (UHF) Gen 2 RFID system. To answer your question, I reached out to Stephen Schwartz, the VP of engineering at RFID Global Solution, an RFID systems integrator and solutions provider. Here is his response:
"The use of different types of circular antennas (left- or right-hand) is generally only required when use cases require the use of bistatic antennas. Bistatic antenna implementations can provide significant performance improvements for difficult-to-read tags whose return signal is being blocked or absorbed, or if the tags are far away from the receiver.
"Bistatic implementations involve one antenna listening while another is transmitting. In this case, the use of different polarization types helps reduce the amount of energy potentially flooding the receiver such that it cannot efficiently hear tag responses. Each reader vendor has a different approach to implementing this feature, so significant testing is required.
"The use of bistatic antennas has become much less common as the performance of UHF RFID readers has significantly improved over the last three years. Receiver sensitivity, isolation between ports, and overall tag-decoding capabilities have improved considerably.
"Most UHF RFID reader vendors now offer cost-competitive readers with four monostatic ports that work well in the vast majority of use cases (dock door, conveyor, forklift and so on). Several offer readers with eight ports providing some combination of monostatic and bistatic capabilities. These are sometimes required for extra-large doorways, or when using battery-assisted tags and other new innovations.
"Your use case will dictate if you really need bistatic antenna implementations. When you deploy, consider using different polarizations. At RFID Global Solution, we look at our customer's use-case requirements and start with one of our previously certified reference designs. We also typically provide a 'cost versus performance' analysis prior to recommending bistatic implementations, due to the added reader and antennas costs associated with these designs."
—Mark Roberti, Founder and Editor, RFID Journal
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