Optimizing Overhead RFID Reader Performance

"Tag reads feed the algorithm"

The key rule to understand when using an overhead RFID reader to determine the location or direction of travel of your RFID-tagged assets is that the more tag reads that are used in the calculation, the more accurate the data.

This is true whether you are using an overhead RFID reader from Impinj, RF Controls, Zebra or any other manufacturer.

Most overhead RFID readers use a linear phased array antenna, which means that there is a certain optimal tag-to-antenna orientation, or read angle, for reading an RFID tag with a single dipole antenna. This leads to a loss in read range and read count if the orientation is not direct ("boresight") as shown in the image below.

The overhead RFID reader will be switching antenna elements so that the tag-to-reader angle will be changing and on at least some of the antenna elements it will be optimal with higher read counts and read range. However, some antenna elements will produce very little, if any, tag reads when reading an RFID tag with a single dipole antenna.

Enter the dual dipole tag antenna

To overcome this issue, there are RFID labels available with a dual dipole tag antenna design, which provides consistent read count performance on every antenna element and reduces the dependence on the read angle.

When using a dual dipole tag antenna, the read performance is much less dependent on the read angle as shown in the image below.

"True" dual dipole design

There are a number of dual dipole designs out there used in labels with a variety of RFID label chips but ultimately the antenna feeds into a single RF input on the chip itself which, while providing similar read performance at any angle, will limit the overall read performance.

The Monza 4 tag chip from Impinj takes this design a step further with its "true" dual dipole design, which uses actual dual RF inputs, resulting in consistent read range at every angle and improved read range compared to other designs.

The benefit of this is illustrated in the image below - note both the consistent read range at every angle and the improved read range versus the dual diploe inlay design performance shown in image 2.

One such example of a label using a true dual diploe design feeding the Monza 4 dual RF inputs is the Confidex Crosswave RFID label.

Summary and considerations

It's recommended to compare the performance of a dual dipole antenna label, such as the Crosswave, with a single dipole or a non-dual RF input chip when using an overhead RFID reader. However, keep in mind that dual dipole antenna design labels tend to be larger and not typically available smaller than 4" x 2".

The cost of most Monza 4 dual inlay labels used to be a consideration but has now become competitive with that of single dipole labels.