Patent ID: 7317378

Claim:
A radio frequency (RF) communication system with a reader and a plurality of ID tags that respond to the reader by sending an identifying code back to the reader upon receiving an interrogating signal from the reader, comprising: a reader for interrogating all of the tags, the reader including a transmitter for transmitting an RF power signal that interrogates the tags, the power signal being on a frequency band and having a center frequency, and the transmitter of the reader having means for sweeping the center frequency of the power signal so that the center frequency varies over time back and forth between a lower frequency and a higher frequency, and the reader including a receiving circuit with a receiving antenna, for receiving a responsive data signal back from each tag interrogated with the RF power signal, and a plurality of RF ID tag devices within receiving range of the reader's power signal, each RF ID tag having a receiving antenna generally tuned to said center frequency of the reader's interrogating RF power signal, a power supply connected to the antenna, with an energy store capable of storing a portion of energy from the reader's RF power signal, received via the antenna, a signal transmitter connected to the power supply for sending out an RF data signal from the tag device in response to being powered by the reader's power signal, and a data source connected to the signal transmitter for generating the data signal, whereby variations from tag to tag in the tuning of the antenna to said center frequency of the RF power signal from the reader, due to manufacturing, environmental or other variations, are accommodated by the sweeping variation of the center frequency of the RF power signal so that at some point in the sweep of the power signal frequency, the antenna on the tag is very closely tuned to the RF power signal.