RFID antenna
Radio frequency identification (RFID) tags have been used in managing inventory, electronic access control, security systems, automatic identification of cars on toll roads, electronic article surveillance (EAS), etc. A typical RFID system includes RFID tags, an RFID reader having an antenna, and a computing device. In RFID systems, the RFID reader communicates to the tags using modulated radio signals, and the tags respond with modulated radio signals. RFID devices including contactless smart cards, contactless tickets, and smart labels have become extremely widespread in recent years. The exchange of information between the contactless card or hybrid contact-contactless card and the associated reader is accomplished by remote electromagnetic coupling between an antenna integrated into the contactless card and a second antenna located in the reader. Antennas are used to radiate and/or receive typically electromagnetic signals, preferably with antenna gain, directivity, and efficiency. RFID tags may be active, containing their own RF transmitter, or passive, having no transmitter. An RFID tag typically includes an antenna system, a power management section, a radio section, and frequently a logical section, a memory, or both. A typical passive RFID tag utilizes an induced antenna coil voltage for operation. This induced AC voltage is rectified and results in a DC voltage. As the DC voltage reaches a certain level, the RFID device starts operating. By providing an energizing RF signal, an RFID reader can communicate with a remotely located RFID device that has no external power source such as a battery. A typical RFID system is made up of reusable transponders or tags fixed to or embedded in product carriers, an antenna system that interrogates the tags via a RF link and a controller. The host (or computer) system interfaces with the controller and directs the interrogation of the tags. Practical antenna design traditionally involves trade-offs between various parameters, including antenna gain, size, efficiency, and bandwidth. The antenna of an RFID reader used in transmitting a carrier signal to an RFID tag is operated in a tuned fashion. The antenna, or coil for low frequency inductively coupled systems, is typically operated in such a fashion that the voltage on the coil is very uniform. The location of the antenna is critical to the interrogation and receipt of the identification code and other data transmitted to and from the tags. The RFID antenna system typically employs a high frequency signal to interrogate the tags and, hence, product carriers which are moved on an interrogation path, such as a conveyor. The antenna system is generally disposed near the interrogation path to provide effective communication to and from the tags. RFID antenna units are typically placed on gate like structures in manufacturing environments and are used to read tagged items as they passed through. The antennas are generally operated in the ranges of 2.45 GHz, 900 MHz or 125 KHz.
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