Frequency diversity transponder arrangement

An interrogator/transponder system, said system comprising:

• a) a transponder, said transponder having
• i. an antenna for receiving a wireless RF interrogation of frequency RF,
• ii. an antenna resonant circuit for deriving a carrier of frequency RF from the power in said wireless RF interrogation,
• iii. a divider for deriving a sub-carrier of frequency SC from said carrier of frequency RF,
• iv. a demodulator for receiving said wireless RF interrogation from said antenna resonant circuit and for providing a demodulated interrogation message at an output,
• v. a controller for receiving said demodulated RF interrogation message at its input and for generating a response message at its output, said response message being generated at said sub-carrier frequency, SC,
• vi. a modulator for modulating said response message upon said carrier to form a wireless response, said modulator being a non-linear circuit element such that said modulated response message has a first channel response centered at frequency FDX1=RF+SC, a second channel response centered at frequency FDX2=RF-SC, and a third channel response centered at frequency FDX3=SC;
• and
• b) an interrogator, said interrogator having
• i. a transmit antenna for transmitting said wireless RF interrogation,
• ii. a receive antenna for receiving said wireless RF response,
• iii. an RF oscillator for generating an uplink RF carrier,
• iv. a modulator which receives said uplink RF carrier and which passes this modulated carrier to said transmit antenna for transmitting said wireless RF interrogation,
• v. a first transformer having a first and a second winding, said first transformer for receiving said wireless RF response from said receive antenna, said first winding of said first transformer being connected to said receive antenna,
• vi. a second transformer having a first and a second winding, said second transformer also for receiving said wireless RF response from said receive antenna, said first winding of said first transformer being connected to said receive antenna,
• vii. a first capacitor in parallel with said second winding of said first transformer, the parallel combination thereof forming a first resonant circuit having a resonant frequency of approximately FDX3=SC whereby said third channel response of frequency FDX3 can be received thereby,
• viii. a second capacitor in parallel with said second winding of said second transformer, the parallel combination thereof forming a second resonant circuit having a resonant frequency of approximately FDX1=RF+SC whereby said first channel response of frequency FDX1 can be received thereby,
• ix. a tuning circuit in parallel with said second resonant circuit, said tuning circuit comprising the series combination of a third capacitor and a switch whereby when said switch is closed, the parallel combination of said second winding of said second transformer and said second and third capacitors lowers the frequency of said second resonant circuit to have a resonant frequency of approximately FDX2=RF-SC whereby said second channel response of frequency FDX2 can be received thereby,
• x. a local oscillator, said local oscillator being enabled to oscillate at frequency RF when the first and second channel responses are to be demodulated and being not enabled when said third channel response is to be demodulated,
• xi. a mixer for receiving the signals from said first and second resonant circuits, and from said local oscillator, said mixer for shifting the frequency of said signals to a common baseband,
• xii. a filter for receiving the output of said demodulator and providing a filtered output signal,
• xiii. a limiter for receiving said filtered output signal and for amplitude limiting said filtered output to form a filtered, limited signal,
• xiv. a demodulator receiving said filtered, limited signal and demodulating therefrom an uplink message, and
• xv. a controller operable to provide data to said modulator for modulation of said uplink RF carder, said controller further operable to receive said uplink message from said demodulator and to enable the operation of said local oscillator.

A method of communicating between a transponder and an interrogator, said method comprising the steps of:

• a) transmitting by said interrogator a wireless RF interrogation;
• b) receiving in a transponder a wireless RF interrogation;
• c) transmitting by said transponder a wireless RF response, said response comprising a first channel response centered at frequency FDX1=RF+SC, a second channel response centered at frequency FDX2=RF-SC, and a third channel response centered at frequency FDX3=SC;
• d) receiving by said interrogator said wireless RF response, wherein a first circuit is operable to receive said first channel response, a second circuit is operable to receive said second channel response, and a third circuit is operable to receive said third channel response,
• e) selecting by a controller the response from one of said first, second, or third circuits, and
• f) demodulating an uplink message from said selected response by a demodulator.