An RFID system consists of three main components: antenna, transceiver (usually combined into one reader) and a transponder (tag). The antenna employs RF waves to transmit a signal that activates the transponder. When activated, the tag sends data back to the antenna. The data is used to notify a programmable logic controller that some form of action should occur. This action could be as simple as opening an access point, such as a door or gate, or as complicated as interfacing with a database to carry out a payment transaction.
Low-frequency RFID systems (30 KHz to 300 KHz) have short transmission ranges (generally a few inches to a few feet). High-frequency RFID systems (3 MHz to 30 MHz) also typically have short transmission ranges. UHF or ultra-high frequency RFID (300 MHz to 1000 MHz) offers longer transmission ranges (several feet to more than 90 feet). The microwave frequencies (1 GHz and above) also provide very long transmission ranges (several hundred feet or more).
In the access control industry, examples of common forms of RFID include low-frequency proximity products (prox cards and readers) operating at 125 KHz, and high-frequency contactless smart card products operating at 13.56 MHz. Examples of common UHF implementations are 433 MHz long-range products for parking collection and 900-MHz long-range products such as cordless telephones. There are also EPC UHF products competing for business in retail, government and supply chain implementations. Microwave products at 2.4 GHz are used for applications such as highway toll collection and wireless networks.