Radio transponder
First Claim
Patent Images
1. A transponder, comprising:
- a transmitting antenna;
a frequency generator and modulator coupled to said transmitting antenna, operative to generate a transmitting frequency from a broadcasted carrier frequency received on said transmitting antenna, and to modulate said transmitting frequency with an information signal;
a receiving antenna;
a demodulator coupled to said receiving antenna; and
a first transmitting frequency suppressor coupled to said receiving antenna operating anti-symmetrically with respect to said demodulator.
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Accused Products
Abstract
A transponder adapted to be used in a checkout or inventory control system is disclosed which transmits by modulating and re-radiating a transponder signal frequency derived from a carrier frequency received on a transmitting antenna. The transponder includes a dual mode antenna and circuitry which selectively operates the antenna to suppress undesired emission of the transponder signal frequency when the transponder is not transmitting. A terminating circuit is further disclosed which suppresses undesired emission of the transponder signal frequency by a demodulator portion of the transponder.
112 Citations
16 Claims
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1. A transponder, comprising:
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a transmitting antenna; a frequency generator and modulator coupled to said transmitting antenna, operative to generate a transmitting frequency from a broadcasted carrier frequency received on said transmitting antenna, and to modulate said transmitting frequency with an information signal; a receiving antenna; a demodulator coupled to said receiving antenna; and a first transmitting frequency suppressor coupled to said receiving antenna operating anti-symmetrically with respect to said demodulator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A low profile transponder, comprising:
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a pair of flat conductor patterns extending generally in loops within said transponder, a first said flat conductor pattern forming a transmitter antenna, and a second said flat conductor pattern forming a receiver antenna, said flat conductor patterns being generally separated from each other by a minimum separation to prevent said receiver antenna from absorbing excessive energy transmitted by said transmitter antenna, said flat conductor pattern forming said transmitter antenna being coupled to a switch at a midsection thereof, said switch including a diode selectively operable to alter a resonant frequency characteristic of said transmitter antenna; and means for transmitting and receiving modulated information signals on said respective transmitter and receiver antennas.
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10. A transponder, comprising:
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a selectively operable dual mode antenna having a first mode resonant at a first frequency, and a second mode in which said first frequency is effectively suppressed; and control means for operating said antenna in said first mode while transmitting and in said second mode while not transmitting. - View Dependent Claims (11, 12)
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13. A system for detecting multiple articles, comprising:
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an interrogator transceiver, operative to transmit an interrogating signal on an interrogator frequency and to receive response signals on a transponder frequency lying in predetermined relation to said interrogator frequency; a plurality of transponders, each attached to an article and operative to transmit said response signal modulated on said transponder frequency identifying each said attached article in turn, each said transponder including a transmitting antenna, controllable to suppress emission of said transponder frequency while not transmitting, and control means operative to switch said transmitting antenna between a transmitting mode and said mode in which said transponder frequency is suppressed. - View Dependent Claims (14, 15, 16)
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Specification