With the decrease in the prices of readers and tags and the expansion of the global market, the application of radio frequency identification RFID (hereinafter referred to as RFID) is increasing day by day. The tag can be powered by the reader (passive tag) or by the tag's on-board power supply (semi-active tag and active tag). As the cost of submicron passive CMOS tags decreases, inventory and other applications increase rapidly. Some evaluations indicate that as the price of passive tags continues to fall, almost every product sold will have an RFID tag inside. Due to the importance of passive RFID tags and the challenges of their unique engineering implementation, this article will focus on passive tag systems.

When receiving the CW signal from the reader, the passive tag rectifies the radio frequency RF (hereinafter referred to as RF) energy to generate a small part of the energy required to keep the tag working, then changes the absorption characteristics of its antenna to modulate the signal, and passes The backscatter is reflected to the reader [see Figure 1]. RFID systems usually use simple modulation techniques and coding systems. However, the spectrum efficiency of simple modulation techniques is low, and for a given data rate, it requires more RF bandwidth. Before modulation, the data must be encoded to form a continuous stream of information. There are many types of bit coding systems available, and each type of coding has its unique advantages in baseband spectral performance, the complexity of the codec, and the difficulty of writing data to memory under clock drive. Because the timing source on the tag board is difficult to achieve the actual required accuracy, as well as challenging bandwidth requirements and maximize RF energy transmission to supply energy to the tag, passive tags have unique requirements for the encoding system used. Finally, some kind of anti-collision protocol is needed so that the reader can read all tags within its coverage.

RFID test summary

Every RFID communication system must pass regulatory requirements and meet the standards used. Today, however, system optimization separates the winner from the loser in this fast-growing industry. This article discusses the testing challenges faced by designers of RFID communication systems: regulatory testing, standards compliance, and optimization.

RFID technology has several unusual engineering test challenges, such as transient signals, bandwidth-inefficient modulation techniques, and backscattered data. Traditional swept-frequency tuning spectrum analyzers, vector signal analyzers and oscilloscopes have been used for the development of wireless data links. However, these tools have some disadvantages when used in RFID testing. Sweep-tuned spectrum analyzers are difficult to accurately capture and characterize instantaneous RF signals. The vector signal analyzer does not actually support RFID modulation technology with low spectral efficiency and special decoding requirements. The fast oscilloscope has a small measurement dynamic range and does not have modulation and decoding functions. The real-time spectrum analyzer RTSA (hereinafter referred to as RTSA) overcomes the limitations of these traditional test tools and has the optimization of instantaneous signals. The patented frequency mask trigger of Tektronix can reliably trigger specific spectrum events in a complex real spectrum environment.

Regulatory testing

Every manufacturer of electronic equipment must meet the regulatory standards of where the equipment is sold or used. Many countries are modifying regulatory regulations to keep up with the unique data link characteristics of passive RFID tags. Most regulatory authorities prohibit CW emission of equipment unless used for short-term testing. Passive tags require the reader to send a CW signal to supply energy to the tag and backscatter to achieve modulation. Even if the passive tag does not have a typical transmitter, it can still emit a modulated signal. However, many regulations do not involve transmitter-based modulation. Various spectrum emission tests are not explicitly included in the reader's RFID standard, but they have become regulations.

Government regulations require that the power, frequency, and bandwidth of the transmitted signal be controlled. These regulations prevent harmful interference and ensure that each transmitter is a friendly neighbor of other users in the frequency band. For many spectrum analyzers, especially swept frequency spectrum analyzers commonly used for pulse signal energy measurement, making such measurements is challenging. RTSA can analyze the energy characteristics of a complete packet transmission process, and can also directly measure the carrier frequency of a frequency hopping signal without placing the signal in the center of a span. At the touch of a button, the analyzer can identify the modulation mode of an instantaneous RFID signal and perform supervisory measurements on power, frequency, and bandwidth, making the pre-compliance test process very flexible and convenient. The pre-compliance test helps ensure that the product passes the conformance test at one time without having to redesign and retest.

Standard conformance

The requirements for reliable interaction between readers and tags are consistent with industry standards such as ISO 18000-6 Type C specifications. This requirement adds many tests beyond the basic requirements to meet the government's spectrum emission requirements. RF conformance testing is critical and helps ensure reliable interoperability between tags and readers.

Pre-programmed measurements can reduce the settling time required to perform these tests. For example, an important measurement of ISO18000-6 Type C is the start-up time and the shutdown time. The carrier energy rise time must be fast enough to ensure that the tag collects enough energy to make it work properly. The signal must also reach a steady state quickly. At the end of the transmission, the carrier energy fall time must be fast enough to prevent interference from other transmissions.

Some RFID devices use an optimized dedicated communication mechanism for specific applications. In this case, engineers need an analyzer that can provide a variety of modulation and coding mechanisms, which can be programmed and adjusted according to the specific format used. [next]


Once the basic specifications are met, it is particularly important to optimize the performance of RFID products to gain a competitive advantage in a particular market space. Performance indicators include the reading speed of the tag, the tag's ability to work in a multi-reader environment, and the distance between the tag and the reader. In consumer applications, the communication speed between tags and readers directly affects user satisfaction. For example, in the public transportation industry using RFID, the reading time was reduced from 5 seconds to less than half a second before it was widely recognized. In industrial applications, speed means production volume: the higher the production volume, the higher the efficiency of the use of capital and human resources. Since passive tags get the energy they need to work properly from RFID readers, multiple readers may cause the tag to try to respond to every reader that interrogates it. In the case of multiple readers, some kind of anti-collision protocol is needed to improve the throughput of the system. Finally, in order to maximize the reading range of the tag, the carrier to noise requirements should be minimized, but this may conflict with the need to prevent the tag from running out of energy by minimizing the carrier's off-time. These optimization measures pose challenges to engineers and measuring equipment.

Let us look at a specific example-optimizing the communication speed, also known as TAT ​​(hereinafter referred to as TAT). The available RF energy, path fading, and changed symbol rate can extend the tag's response time to reader queries. The slower the response, the longer it takes to read multiple tags. Rapid measurement of TAT is necessary to optimize the speed of the RFID system.

TSA can be easily measured using RTSA. First, you need to install a frequency template trigger to get the entire query between the tag and the reader. RTSA's power versus time view allows users to watch the entire launch process. It is customary to think that the time between the end of one downlink transmission (from the reader to the tag) and the beginning of the next downlink transmission is the TAT of the half-duplex system. Put a marker at the end of the tag query, and the second δ marker at the end of backscattering or the beginning of the next data transmission from the reader to accurately measure the TAT time. Maintaining the shortest TAT under the conditions of a large-scale downlink will help maximize system throughput.

RTSA can also demodulate symbols or bits related to tag queries. The user only needs to select the corresponding RFID standard, modulation type and decoding format. The analyzer can automatically detect and display the link bit rate. In order to further improve the engineer's production efficiency, the function-based color coding (color-coded) is performed on the recovered data symbols. RTSA can automatically recognize the leading symbols and dye those symbols yellow. This makes it easy to identify the actual data load and compare it with known values.


The RFID industry contains a large number of technologies and applications, many of which are different from typical communication links. Engineers need tools that can quickly and easily perform regulatory testing, standards compliance, and optimized measurements.

RSA3408A is a tool to meet these needs, supporting multiple RFID international standards, time-related multi-domain measurements, customized RFID communication systems, and demodulation and symbol decoding of multiple RFID signals. The instrument greatly improves engineering efficiency and shortens the time to market. Whether it is to meet government spectrum regulations, to ensure that tags or readers meet specific communication standards, or to debug a problem encountered in development, RTSA is a unique tool for analyzing RFID signals emitted by readers and tags.

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