Interrogator Construction

An RFID interrogator works as a transmitter as well as a receiver of radio frequency (RF) signals. A signal is broadcast and received through antennas that are connected to the interrogator. This is all you would generally need to know in order to be able to use the interrogator in your RFID system. However, for those who are always asking how things work and why, I am including a description of the interrogator's components and their function.

An interrogator consists of an RF transmitter and RF receiver (these two components are sometimes called an RF module), a control unit (basically a computer), and communication channels going to the antenna, as well as network or peripheral devices. Sometimes there is a circulator, which is necessary for function of a mono-static antenna (a single antenna used to broadcast and receive from the same antenna port).

The RF transmitter consists of the following:

• An oscillator that creates a carrier frequency, which is the frequency the reader is operating on.

• A modulator that modulates the carrier wave from the oscillator in order to include commands or data intended for the RF tag.

• An amplifier that amplifies (strengthens) the signal before it is transferred to the antenna. The antenna then broadcasts this signal to the tags in the environment.

The RF receiver includes these components:

• A demodulator, which extracts data from the received signal that comes from the tag through the interrogator's antenna.

• An amplifier, which amplifies the demodulated signal before it is sent to be processed by the control unit.

The control unit contains the following:

• A microprocessor (and controller) that controls the function of an interrogator, governs data transmissions, processes and filters the received data, sends data via a network to the middleware or back-end applications, manages various I/O devices, receives commands from middleware or other applications, and communicates with memory.

• Memory in the form of random access memory (RAM) and read-only memory (ROM) that carries an operating system such as Linux or Windows CE. Many times there is a data storage, which is equivalent to a hard drive in a computer, which captures operation logs and data transferred to and from the tag.