The Multitag Microwave RFID System with Extended Operation Range

The Multitag Microwave RFID System with Extended Operation Range

Igor B. Shirokov (Sevastopol National Technical University, Ukraine)
DOI: 10.4018/978-1-4666-1616-5.ch010


The problems of radio frequency identification are discussed. It was shown that the use of passive transponders is preferable, but weak energy of system in this case reduces the operation distance and decreases the noise-immunity of the system. The problems of traditional radio-frequency identification systems are discussed. In this chapter the use of homodyne method of useful signal selecting was proposed. The augmentation signal of transponder was obtained by means of frequency shift with the help of controlled phase shifter. This solution allows to increase the energy and the noise-immunity of the system (the operation distance is increased). Furthermore, the interrogator can treat several transponders simultaneously in this case. Additionally the use of one-port transistor amplifier for increasing of operation range was proposed. The energy consumption of such amplifier and its cost are very low, but the gain of amplifier can reach 20 dB and more.
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Understanding Of Problems Of Conventional Rfid Systems

Harmonic RFID System

Functioning of the RFID system assumes a sending of a probing pulse with the help of transceiver of basic unit which activates a transponder, established on the object. Transponder replies by the reciprocal radio-frequency pulse modulated by a unique identification code. The use of passive transponder represents the greater interest for consumers, as its power supplying is carried out due to the energy of a signal of basic unit within the communication time. Under clear reasons the link of such system should be duplex. Due to the increased power of such communication link, there is an opportunity in this case to send several commands to transponder and to organize, thus, any necessary exchange protocol.

The organization of duplex channel involves the engineers in complicated design of transponder and increases its cost. In practice there are widely used so-called harmonic RFID systems (Colpitts et al, 2004) and (Vanjari et al, 2007) in which the transceiver of the interrogator sends initial signal on one radio frequency, and transponder responds on frequency, which is multiple to the initial one. As a rule, frequency rate is equal to two. Such approach satisfies the main principle of duplex communication. On the other hand the doubling of frequency allows us to use the same known antenna for reception and radiation. Multiplication of frequency of the transceiver can be achieved by the elementary technical solution, for example by connection to the terminal of the transponder’s antenna of Shottki diodes, as it is shown on Figure1 a.

Figure 1.

Transponder circuit scheme a), Spectrogram of combinatorial RFID system b)

Besides the multiplication of interrogator signal frequency, they make its rectifying for transponder modulator feeding. Obviously, the energy of signal, which is received from interrogator and rectified, is weak, and this signal must be presented during entire communication session. The Shottki diodes let us minimize the losses and the real value of rectified voltage can reach few volts. That is enough for the feeding of modulator.

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