UHF RFID Readers
UHF RFID readers use radio-frequency waves to wirelessly transfer data between a reader and a tag/label in order to identify, categorize and track assets. They are used in asset management, e-commerce and a number of other applications.
A UHF RFID reader consists of an RF front end, an antenna and a transmitter/receiver. This article focuses on an Analog Devices’ signal chain-based UHF RFID reader RF front end that meets China’s standards for electronically identifying motor vehicles.
RF Front End
A UHF RFID reader’s RF front end is the circuitry between the receiver Antenna input and the mixer stage. This includes the transmitter modulator, PLL/VCO, and receiver baseband filter and PGA. It also includes the demodulator and the low noise amplifier (LNA).
The RF front end is critical to the functioning of an RFID reader. This is because it is responsible for receiving and demodulating a signal from the transmitter, and sending the received signals to the antenna tuner for processing and transmission. It also provides the isolation between the transmitter and receiver to reduce the self-interference from the antenna.
There are several types of RF semiconductor technologies available to implement the RF front end. Each one corresponds to different RF functions and applications.
In this paper, an integrated solution based on the AD9361 is analyzed to implement an UHF RFID reader RF front end. It is significantly simplified compared to discrete two-component solutions, and meets the GB/T 29768-2013 and GB/T 35786-2017 requirements with reduced receiver sensitivity.
To demonstrate the UHF RFID reader RF front end, an SJC circuit including the adaptive SJC algorithm is implemented. This circuit uses the AD9963 and ADF9010 to integrate the transmitter modulator, PLL/VCO, receiver baseband filter and PGA. It is also used with the ADL5523 LNA to provide low noise figures and high gain. The 75 dB high dynamic range RF detector LT5538 is also included for the purpose of testing the SJC RF power detector.
ADI’s AD9963 integrates a 12-bit low power MxFE(r) converter that provides two ADC channels sampling at 100 MSPS and two DAC channels sampling at 170 MSPS. It is a fully integrated RF transmitter modulator, local oscillator (LO), and receiver analog baseband front end.
The AD9963 also integrates the ADL5523 LNA, which is designed to provide low noise figure, high gain, and high linearity. The receiver gain is set to 24 dB. The NF is less than 3 dB for the entire system.
The ADF9010 is a fully integrated RF transmitter modulator, LO, and receiver analog baseband front end that operates from 840 MHz to 960 MHz. The ADL5382 is an RF modulator and a demodulator that is included on the evaluation board.
Antenna Design
The antenna design of a UHF RFID reader is an important part of the reader’s overall design. The antenna must be designed to maximize the range of the tag’s read signal, as well as transmit and receive power efficiently.
The main challenge for an antenna in an RFID system is to maximize the power transfer between the reader and the tag, which can be achieved by achieving a high transmission coefficient. In addition, the gain of the antenna should be optimized so that the tags can be detected by the reader irrespective of their physical orientation.
To meet these requirements, the antenna design should be based on a predefined structure. This can be achieved by optimization, which is a process that uses mathematical models to optimize the RF performance of a design.
Various parameters can be used to modify the antenna design such as the length of the t-matching network, slots, and the dielectric loss tangent. In addition, the antenna curvature can be manipulated to improve the RF performance.
In this paper, we design a small electrically-slim and flexible passive tag antenna operating at the European and US UHF RFID bands. The small antenna has dimensions of 13 mm x 28 mm x 0.35 mm, and its UHF RFID Reader geometry was optimized using a Genetic Algorithm to maximize the read range of the tag.
As a result, the tag antenna achieves a maximum gain of 8.9 dBi and has a resonant frequency of 950 MHz. In addition, the antenna per-formance on flat and curved surfaces was evaluated by simulations of input impedance, reflection coefficient, gain, and read range.
Furthermore, the antenna performance is compared with that of a commercially available UHF RFID reader. The results show that the proposed reconfigurable reader antenna offers similar features as the commercial one, but it provides a larger coverage area for passive RFID-based applications.
The reconfigurable reader antenna can radiate four independently switchable radiation beams in the azimuth plane, depending on the position of the user. This allows the reader to detect the presence of multiple tags. It is easy to fabricate and provides increased flexibility in RFID-based applications.
Transmitter
UHF RFID readers are a great option for applications that require long range and high data rates. They are also available in a variety of form factors and are suited to embedded systems. They are usually designed for use with a wide range of tags, making them a great choice for applications that need to integrate easily with other devices in the system.
The transmitter is a key part of any UHF RFID reader, as it carries information about the tag and its contents to the receiver. It is therefore important to ensure that the transmitter is capable of establishing an effective and reliable RF link with the tag.
Transmitter performance is dependent on a number of factors, including the antenna gain, TX output power and RX sensitivity. In addition, there are many regulatory requirements affecting the frequency, channel schemes and interface/co-existence rules.
Compared with barcode and HF bands, UHF RFID is capable of tracking objects longer and more accurately, at lower costs, in a wider range of locations, and at different points in the object’s life cycle. This makes it an attractive technology for a variety of applications, such as inventory management, asset tracking, supply chain automation and security.
Although the RFID industry is constantly advancing, there are still a number of limitations to this technology. One of the major limitations is the transmitter’s RF performance, especially in the presence of interference and fading.
To address this issue, the UHF RFID reader RF front end is designed with a low noise digital modulated power amplifier (DPA). The DPA enables I/Q digital signals to be directly modulated and eliminates the pulse shaping filter, up-conversion mixer and power amplifier driver that contribute much of the TX noise in a conventional RFID transmitter.
The DPA is able to provide a low TX noise, stable output power and a high level of accuracy through a series of optimizations. The DPA is based on a CMOS process, which provides increased integration and reduced costs in comparison to discrete components.
UHF RFID is a great solution for asset management applications, but it can be difficult to select the right technology. Choosing a system based on the frequency, cost and form factor of a tag can lead to poor results and an overall system that doesn’t meet the needs of your business.
Receiver
The receiver is the part of a UHF RFID reader that receives and processes the backscattered signals of passive RFID UHF RFID Reader tags. It also translates the signals into more operational data. It is essential for a UHF RFID reader to be accurate and efficient.
The reader must be able to read the backscattered signal of each tag within its range, which is usually tens of meters. This is important for applications that require high accuracy and speed, such as inventory management or POS systems.
A UHF RFID reader can detect multiple tags at once, making it easier to monitor large areas and keep track of products throughout the supply chain. This makes it an ideal choice for a variety of industrial, consumer, and medical applications.
Unlike HF readers, which can only read up to a few meters, UHF systems can read tags up to twelve meters away. They can also transmit and receive at a faster rate, enabling transactions to occur more quickly.
However, these advantages come with disadvantages. One of these disadvantages is that UHF radio waves can penetrate metal surfaces, such as a steel shelf, and can even be used to identify liquids stored inside bottles. Another issue is that UHF RFID readers often suffer from poor transmitter-to-receiver isolation, which means that the CW signal transmitted by the reader will leak into the tag’s signal.
This causes a decrease in the receiver’s sensitivity. To avoid this issue, some UHF RFID readers use separate transmit and receive antennas. This increases the isolation between the antennas, but adds to the cost and complexity of the device.
In addition, UHF RFID readers must meet a number of performance requirements. These requirements are specified in GB/T 29768-2013 and GB/T 35786-2017. These standards include a link budget, a key technique in RFID such as SJC, and a number of RF performance requirements.
Analog Devices offers two implementations of its signal chain-based UHF RFID reader RF front end, both of which meet these standards. The first implementation is based on the ADF9010 and AD9963, while the second is based on the AD9361.