Patent ID: 7936268

Claim:
A system comprising: an antenna system having a single antenna structure, the single antenna structure having a first feed point coupled to a first capacitor, and a second feed point coupled to a second capacitor, wherein the first feed point transmits a first interrogation signal in response to a first antenna current and the second feed point transmits a second interrogation signal in response to a second antenna current; an antenna communication circuit configured to output an alternating current signal having an average value of zero; a first current source coupled to the antenna communication circuit and configured to output a first direct current signal responsive to an antenna selecting signal from the antenna communication circuit, wherein the first direct current signal has a greater magnitude than a peak-to-peak value of the alternating current signal; a first diode coupled to the antenna communication circuit to receive the alternating current signal, and coupled to the first current source and the first capacitor, wherein the first diode is forward biased by the first direct current signal to output a first diode alternating current signal with a first direct current component to the first capacitor, the first capacitor removing the first direct current component from the first diode alternating signal to provide the first antenna current to the first feed point; a second current source coupled to the antenna communication circuit and configured to output a second direct current signal responsive to an antenna selecting signal from the antenna communication circuit, wherein the second direct current signal has a greater magnitude than a peak-to-peak value of the alternating current signal; and a second diode coupled to the antenna communication circuit to receive the alternating current signal, and coupled to the second current source and the second capacitor, wherein the second diode is forward biased by the second direct current signal to output a second diode alternating current signal with a second direct current component to the second capacitor, the second capacitor removing the second direct current component from the second diode alternating signal to provide the second antenna current to the second feed point.