TABLE OF CONTENTS An RFID reader is, at heart, a radio transceiver: a transmitter and receiver that work together to communicate with the tag. As such, it faces the same challenges all radios encounter, plus a few specialized problems unusual in wireless communications but well known to practitioners of other passive communication technology, radar.
Every radio transmitter must deliver:
Accuracy: the transmitter must accurately modulate the carrier frequency with the desired baseband signal and maintain the carrier at the desired frequency.
Efficiency: the transmitter must deliver this undistorted signal at the desired absolute output power without wasting too much DC power. The final amplifier of the transmitter is often the single largest consumer of DC power in a radio.
Low spurious radiation: distortion of the transmitted signal can lead to radiation at frequencies outside the authorized bands, which potentially can interfere with licensed users and is frowned upon by most regulatory authorities. (We'll discuss in more detail how this spurious output arises in Section 4.3 of this chapter.) Production of clean, spur-free signals is often a trade-off between the amount of RF power to be transmitted and the amount of DC power available for the purpose.
Flexibility: the transmitter should turn off when not in use to save power and avoid creating a large interfering signal, and turn back on again quickly, so as to be responsive when there are tags to be read.
Any radio receiver needs to provide:
Sensitivity
