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Do I have to use opposing polarity RFID antennas?

Posted by Michael Crudele on



Today, we had a client contact us because they had an installation of S9028PCL96RTN circularly polarized RFID antennas that were suffering from poor performance.  The use case was a portal set up in a hallway to track employees coming and going from a job site.  The RFMAX 8.5 dBic, 10x10 inch,  circular polarized RFID panel antennas were set up on both sides of the portal (which was about 4 foot wide) and the antennas were arranged such that they were DIRECTLY opposite on another.


Apparently, each time they turned on the Impinj R420 RFID reader and activated the antenna ports, they were having major trouble reading RFID tags.  However, when they de-activated all of the antennas on one side of the portal, they experienced INCREASED performance, thus leading us to believe that the antennas from one side of the portal were interfering with those on the opposing side.  After investigating, we discovered that all of the circular polarized RFMAX antennas they were using were of the same polarity, in this case, LHCP.


For maximum performance, RFID antennas should not be positioned directly across from each other.  They should always be off-set from one another, if at all possible.  In addition, when antennas MUST be positioned directly across from each other, in close proximity (< 12-15 feet apart) that is the only time that opposing polarities SHOULD be used.  In this use case, it is quite possible that the antennas are interfering with one another and canceling out signal.  So, there are two possible corrective actions:

1. Remove all of the antennas from one side of the portal and replace it with antennas of opposing polarity, in this case, RHCP antennas.

2. Without swapping out the antennas, they can try simply changing the articulation of each set of antennas, if the mounting hardware allows this.  For these 10x10 inch antennas, I'd recommend using the fully articulating RFMAX EZM6COMBO antenna mounts.


To clarify, what I mean is this…take all of the antennas on the left side of the portal and articulate / position them at a slight angle towards the outside door.  Next, take all of the antennas on the right side of the portal and articulate / position them at a slight angle away from the outside door.  By not having the antennas facing each other directly, they should be able to eliminate a significant amount of interference.


If you have an RFID or other antenna related question, please call us at 1-888-925-5967 or contact us here.


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