RJ Burkholder, Research Professor of Electromagnetics and RF at The Ohio State University
In the real world, RFID systems rarely have 100% reliability. System designers for years have tried to tweak their solutions to get closer to this goal. Unfortunately, their improvements remain unsatisfactory because they are usually tweaking in the wrong place.
A typical UHF RFID system is illustrated below:
It has four basic components: 1) the reader, 2) the computer that controls the reader, 3) the tags, and 4) the antenna. So, what does the designer really have control over? Let’s start with the reader. Today’s RFID readers have many options: power output, power-over-Ethernet, Wi- Fi, various coding and data collection software, GPIO switches, and multiple antenna ports, to name a few. These options mainly have to do with the particular application, and are very helpful for keeping costs down, but for the most part all readers operate on the same basic principle and have similar performance when it comes to tag reading.
The computer. Probably the biggest investment in RFID development has been in software. Good software is absolutely essential for handling the massive amount of data available from reading thousands of tags. Software also provides added functionality to RFID. It is possible to implement algorithms that can estimate things like tag location and even changes in the tag environment. But, again, software cannot improve the basic tag reading performance of a system (although software can definitely have an effect on the speed of a system). Regardless, the software is often outside the scope of the RFID system designer anyway.
The tag. There are many, many variations in passive UHF RFID tags alone. The variations are mainly for the particular applications. General purpose tags work great in empty air, but start to degrade when placed close to materials. Tags for metal surfaces must be specially designed or they won’t work at all. Very often tags must be embedded inside a card or label or even a tire. All of these things affect the read performance, and are very important to consider in RFID systems, but unfortunately the tag and where it is placed is often outside the control of the system designer.
To summarize, the computer software and tags are often not the responsibility of the system designer and are very limited in how much they can improve read performance. Readers are pretty well standardized and can affect cost, but don’t really improve performance. So what can the designer really do?
The antenna. This brings us back to my assertion that the antenna is the most important component of a UHF RFID system. Of course, all four components are essential, but the antenna may be the only thing the system designer can really manipulate to improve performance. Oddly enough, it is also the most overlooked component. In my opinion, the reason for this is simply a lack of education on how antennas work and how the electromagnetic field radiated by an antenna fills and penetrates a given space. The main issues are polarization, fading, attenuation, gain, maximum EIRP (effective isotropic radiated power) and diversity.
A good understanding of these issues will aid the designer in selecting the type and number of antennas, and where to put them for optimum performance. My goal for the next several blogs is to educate the reader about antennas and antenna placement, and provide tips and examples that can be applied in real world applications. All this is needed to truly understand the uniqueness of the NeWave® Wave® antenna.
Next blog: Antenna basics – gain and EIRP
 The opinions expressed on this webpage are the author’s and do not necessarily represent the opinions of The Ohio State University.