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RFID Antenna Basics – Gain and EIRP

RJ Burkholder, Research Professor of Electromagnetics and RF at The Ohio State University1

In the last blog I maintained that the antenna is the most important part of a UHF RFID system (see figure below). This is because the computer software, reader, and RFID tag are quite optimized now, and often outside the control of the system designer/integrator. Performance improvements must come from the antenna and its deployment.

A typical UHF RFID inventory system

Before getting into the fine art of antenna deployment, it is first necessary to understand the basic principles of 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.

The most basic characteristic of an antenna is its gain. This number is defined as the amplification of the antenna compared with an antenna that radiates equally in all directions. Hence, the units of gain are often dBi, which means “decibels relative to isotropic”. By definition, an antenna that has greater than 0 dBi gain does not radiate isotopically (the same in all directions), but has a gain pattern, sometimes referred to as its antenna pattern, or directivity pattern, as illustrated below.

image2Gain patterns of a broad beam antenna and a narrow beam antenna.

The narrow beam antenna has a higher gain than the broad beam antenna, but a much smaller angular coverage. This is because both antennas radiate the same total power, and the gain pattern determines how this power is distributed. (Note that I am assuming here for simplicity that the antennas are 100% efficient. In other words, all of the power input to the antenna is radiated.) Our first principal is this:

  1. For the same amount of radiated power, increasing the gain of an antenna decreases the angular coverage.

A typical patch-type RFID antenna has a gain of about 6 dBi and looks like the broad beam pattern above. The designer might like to improve the read range by using an antenna with a higher gain, like the narrow beam antenna above, if angular coverage is not important. Unfortunately, it’s not that simple, but not because of the antenna.

This brings us to a very important concept in UHF RFID, namely, Effective Isotropic Radiated Power (EIRP). EIRP is defined as the amount of power that a theoretical isotropic antenna would emit to produce the peak power density observed in the direction of maximum antenna gain. For example, a typical RFID reader generates 30 dBm (decibels relative to a miliwatt) of RF power. Connecting a patch antenna with 6 dBi gain results in an EIRP of 36 dBm (30+6).

It so happens that 36 dBm is the maximum EIRP allowed by the FCC for electronic devices in the UHF RFID band. Now suppose I want to use the narrow beam antenna shown above, which has a gain of 12 dBi for example. Then the EIRP becomes 42 dBm which is over the FCC limit. I will have to reduce the reader power to compensate. Our second principal is this:

  1. Increasing the gain of an antenna also increases the EIRP, which is limited by the FCC.

Therefore, for maximum read range it doesn’t necessarily help to use a high gain antenna because you will have to reduce the RF power. The only advantages of a high gain antenna in RFID is to get a good read range with minimal power, or to focus a beam in a limited coverage area.

Next blog: Antenna basics – polarization: does it really matter?

1 The opinions expressed on this webpage are the author’s and do not necessarily represent the opinions of The Ohio State University.

Smart Shelf™ & The Internet of Things

Author: Dr. Den Burnside CTO and Founder of NeWave® Sensor Solutions and Emeritus Professor at the Ohio State University

NeWave® Sensor Solutions was recently interviewed for  the  Discovery Channel’s  new web and Facebook program: “Technology is Changing How We Live ” ,sponsored by DeVry University. NeWave’s Smart Shelf™ was selected by the Discovery Channel  to showcase future technology in “Cashier Free Retailers” and as an excellent example of a smart device enabling the  Internet of Things (IoT).  We recommend opening links in Internet Explorer.

Why is that important? Let’s examine what is the definition of the Internet of Things and the attributes of NeWave’s Smart Shelf.

 “Internet of things
From Wikipedia, the free encyclopedia
Drawing representing the Internet of things

The Internet of things (IoT) is the inter-networking of physical devices, vehicles (also referred to as “connected devices” and “smart devices“), buildings, and other items—embedded with electronics, software, sensors, actuators, and network connectivity that enable these objects to collect and exchange data.[1][2][3] In 2013 the Global Standards Initiative on Internet of Things (IoT-GSI) defined the IoT as “the infrastructure of the information society.”[3] The IoT allows objects to be sensed or controlled remotely across existing network infrastructure,[4] creating opportunities for more direct integration of the physical world into computer-based systems, and resulting in improved efficiency, accuracy and economic benefit in addition to reduced human intervention.[5][6][7][8][9][10] When IoT is augmented with sensors and actuators, the technology becomes an instance of the more general class of cyber-physical systems, which also encompasses technologies such as smart grids, virtual power plants, smart homes, intelligent transportation and smart cities. Each thing is uniquely identifiable through its embedded computing system but is able to interoperate within the existing Internet infrastructure. Experts estimate that the IoT will consist of almost 50 billion objects by 2020.[11]

Of course, that estimate for 50 billion objects is referring to devices connected to the internet. In this case, many see the future of the internet as being between machines without human intervention, which is described as being machine-to-machine (M2M) communication. Obviously, these machines must operate in autonomous mode in that there is no human involved. Besides being M2M, there are many attributes associated with the IoT such as being seamless, scalable, minimal impact on web, provides valuable data and associated analytics, and web installation and maintenance. All of these features have been incorporated into our Smart Shelf solution.

Let us examine each of these attributes in terms of our Smart Shelf solution

NeWave’s Smart Shelf™ system provides information on shelf item movement to prevent merchandise out of stocks using its unique patented Wave® RFID antenna technology. In simple terms, when an item leaves the shelf, NeWave’s Smart Shelf sees it even when it is not tagged. Based on criteria set by the retailer for low inventory limits, the Smart Shelf software signals an alert in real time that can be sent on-site to store managers, or remotely to merchandising and loss prevention personnel as well as suppliers. There is no need to tag items, so you get all the benefits of the solution, without the added labor, item tag and maintenance costs.  The Smart Shelf can also trigger an audio alarm message and a video capture alert within the store. The system strives to make it easy to get real time in or out of stock shelf information available anytime to any authorized person or group.

To grasp this connection between Smart Shelf and IoT, one has to understand better how our Smart Shelf solution works from start to finish. First, our patented NeWave reader has been specifically designed for Smart Shelf applications in that it is based on an embedded small board computer as opposed to a simple microprocessor used by other RFID readers. This is extremely important in that the Smart Shelf reader must collect all the RFID tag data, process inventory data, compress the inventory data and then transfer data to the customer. Since all these functions require significant software and multiple processes that vary with application running at the same time, it must be done within a computer and not a simple microprocessor. As a result, our reader comes with a complete set of Smart Shelf middleware and network software dramatically reducing solution installation complexity time and cost. In fact, the NeWave reader network software is designed to optimize the system performance and cost by employing the following powerful IoT attributes:

  1. M2M: Our NeWave reader is uniquely designed for Smart Shelf based on its embedded small board computer. It autonomously sends the compressed product inventory data directly to the customer’s server in a form that the customer can directly use within their existing inventory database. Thus, the customer defines the data format and transfer process making it ideal for their operation. As a result, the user has more timely and accurate shelf inventory data.
  1. Seamless: It is very difficult to design a system that is virtually seamless in that everything must continuously flow without human interruption from start to finish. For Smart Shelf, one simply connects the NeWave reader to the Smart Shelf hardware and then powers-up the reader. As our reader is powered-up, it automatically connects to the VPN Admin Server in NeWave’s Innovation Center. The reader is able to immediately connect in that we have pre-loaded the proper credentials into each reader. Once NeWave’s Admin server receives this initial credential information, it adds this reader system to its operational systems. In return, the Admin server sends a request to the installer to properly define his or her information, location, etc. The installer completes this form and then is informed to install the complete system using a bar code scanner interfaced to the reader. Once the installer completes the installation using the bar code scanner, the reader will automatically process this information and send an initial planogram file to the Admin Server. This initial information includes the product UPC code, product location and associated RFID tray identification number. Once this file is received at the Admin Server, it will take this information and add the product name and dimensions. This will complete the planogram file that is automatically sent back to the reader as well as being stored on the Admin server. When this file comes back to the reader, it will start the normal inventory data collection and the installer will be informed that the installation has been completed; this process takes only minutes.  During the normal operation, the reader automatically checks itself, determines any maintenance issue and sends this information to the Admin server. Once this maintenance information is received at the Admin server, all the reader maintenance is performed over the web unless there is a hardware failure. If it is a reader hardware failure, the reader can be fully corrected by removing the SD card from the old reader and placing it into the new reader. Once this is done, the new reader will fully replace the old one. If the maintenance is associated with the Smart Shelf hardware, it can easily be corrected using the maintenance option with the bar code scanner. Finally, the main objective of Smart Shelf is to eliminate out-of-stock. This is done by the reader automatically sending restock information to store personnel using a local NeWave Wi-Fi network within the store. Thus, the Smart Shelf system is a seamless solution.
  1. Scalable: Smart Shelf is designed to take advantage of our patented Wave® antennas that have been designed to cover a zone such as a 3’ or 4’ wide shelving section. The zones can be designed independently as adjacent or non-adjacent sections. The software has been designed so that each reader connects directly to the customer, Admin server and the local store network. Thus, each NeWave reader has software installed and operated in the same form making the software scalable as well.
  1. Minimal Impact on Web: The IoT becomes effective as more and more systems are attached to the web. This sounds great, but one has to be concerned about the impact on the web as these systems are added and sending important inventory data coming from 1000’s of our reader systems taking up huge amounts of bandwidth.. In our case, the middleware processing within our reader optimally compresses the inventory data and only sends this very limited data on inventory changes a few times per day greatly reducing the amount of bandwidth required. Further, the customer takes this very limited data and integrates it within their existing database.. Therefore, the customer storage is virtually the same as used previously. The Admin server does not keep any inventory data. It simply stores the store information, shelving planogram and needed maintenance issues. Therefore, it can easily handle a very large number of reader systems. Finally, the store re-stock information is stored in the reader and cleared as each product is re-stocked. Thus, there is very minimal impact on the web even though we may be running 1000’s of readers at one time.
  1. Provide Valuable Data: Our Smart Shelf system provides very valuable information to the customer. For example, the customer can determine the actual product inventory versus time. This can be used to determine very accurately when and what products need to be manufactured in very timely way. Or, it can determine how well their products are re-stocked. Therefore, customers can be using “just-in-time” stocking of their products that will result in tremendous savings and a very positive return-on-investment. Finally, forensic analytics can be used on this inventory data to provide a whole set of new information such as season impact, weather impact, local customer habits, the impact of promotions and new products, etc. As the historical database grows the value of the inventory data collected will as well providing greater and greater business insight to the retailer and manufacturer.
  1. Web Installation and Maintenance: The middleware within the reader automatically knows if the Smart Shelf system has been installed or not. If not as stated earlier, the installer will simply be notified to start the Smart Shelf installation using the bar code scanner. Once this scanning process is completed, the Smart Shelf planogram is stored in NeWave’s Admin server and reader. This is an automatic process done over the internet as explained earlier. The Smart Shelf maintenance is performed by first using the bar code scanner to interrupt the reader from its normal operation. Once the maintenance person has been informed that the reader is now in maintenance mode, he or she can begin the various maintenance functions by using the bar code scanner. Note that once the maintenance is complete, the reader will again automatically upload the new potential planogram to the Admin server. The Admin server will again add the product names and dimensions and send this complete planogram file back to the NeWave reader. Note that this complete planogram file will then be stored in the reader and Admin server. Once these steps are complete, the reader will again return to normal inventory data collection.The NeWave reader comes with our unique middleware and software pre-loaded at no additional cost. The reader and Smart Shelf must be monitored by the NeWave Admin server as described earlier. This becomes a very important function in that the reader will automatically notify the Admin server of any system failure for immediate resolution. Since any failure of the reader short of a hardware failure can be corrected over the web, the customer can be assured that the system is functioning properly 24/7. This IoT benefit will be provided to the customer at a minimal monthly expense per system.
  1. Sensor Fusion: The seamless process used for Smart Shelf also takes advantage of sensor fusion in that we are using RFID to collect inventory data but we also use a bar code scanner process to do the installation and maintenance. Using this approach, we are taking advantage of the more valuable attributes of multiple sensors to create the best possible overall Internet of Things solution.

In summary, NeWave’s Smart Shelf has taken full advantage of the IoT attributes to create a unique cost-effective, reliable, accurate and easy to install and maintain shelf inventory solution that eliminates out-of-stock for each individual product placed in our Smart Shelf dispenser trays. NeWave’s Smart Shelf is unique in function and performance to prevent Out of Stocks offering a very significant business opportunity for retailers to enter the world of IoT.

Why the Antenna is the Most Important Component of an RFID System

RJ Burkholder, Research Professor of Electromagnetics and RF at The Ohio State University[1]

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

[1] The opinions expressed on this webpage are the author’s and do not necessarily represent the opinions of The Ohio State University.

A New Paradigm for Item-level RFID Antennas

Author: RJ Burkholder, Research Professor of Electromagnetics and RF at The Ohio State University

For years RFID system designers have trusted in the old reliable patch antenna to solve all their reader antenna needs. But how reliable is it? If you were to picture the beam, it would look something like a single beam, conical spotlight illumination pattern:


This might be good if you’re looking for tags that are far away and in a specific and known location, but not good for tags that may be close to the antenna but outside the beam. Also, in most portal and item-level applications you don’t want to see tags that are far away, extraneous tags, because that makes it difficult to localize the tags of interest.

What’s the solution? Well, we can crank down the power on the RFID reader, but that doesn’t solve the spotlight problem because the beam simply collapses in the same pattern. We can use more antennas to try and fill in the gaps in the illumination, but that is a Band-Aid solution at best, one never really knows if all the gaps are covered and it becomes a complex and expensive solution. Another possibility is the so-called “near-field antenna” (an oxymoron to antenna designers), but these have a very limited range, too limited for item-level RFID and they are not practical for covering large volumes.

The NeWave® philosophy is to not use a spotlight to do the job of a fluorescent light. The latter does a much better job of uniformly illuminating a room or in the case of item-level RFID, the targeted tag read zone. By analogy, NeWave’s Wave® antenna is designed specifically for reliable high-diversity high-density coverage of a finite volume around the antenna, perfect for item-level RFID:


It’s what we call a “distributed antenna” because it emanates waves all along its length like a fluorescent lightbulb. It also uniquely creates five interlocking beams traveling in different directions to provide much better polarization diversity than a single beam patch antenna. This design is ideal for item-level applications because tags can be localized to a certain volume around the antenna, and there are no gaps in the coverage.  Unlike the patch, due to the Wave’s illumination pattern, tags can be read regardless of their orientation.

The concept of an antenna that creates localized coverage of a given volume is a new paradigm for item-level RFID applications. It enables the establishment of zones within a larger environment such as a warehouse or retail store, making it possible to accurately locate tags quickly and perform inventories at the push of a button, the Holy Grail of item-level RFID technology.  Importantly the size of these zones can be adjusted from approximately 2 to 10 feet by a simple power adjustment providing great flexibility.

Next blog: Why the antenna is the most important component of an RFID system.

The opinions expressed on this webpage are the author’s and do not necessarily represent the opinions of The Ohio State University.