Surveillance and identification system antennas
First Claim
1. In a system for article surveillance and identification, an antenna system comprising:
- interrogating transmitting antenna means for radiating an electromagnetic interrogation signal at a center frequency and having an elliptical polarization in a first-handed direction;
transponder antenna means for receiving said electromagnetic interrogation signal and reradiating a modified electromagnetic interrogation signal having a linear polarization; and
,interrogating receiving antenna means for receiving said modified electromagnetic interrogation signal at substantially said center frequency and having an elliptical polarization in a direction opposite to that of said first-handed direction.
1 Assignment
0 Petitions
Accused Products
Abstract
An antenna system (20) in transponder article surveillance and identification system (10) employs a separate interrogating transmitting antenna (31) and interrogating receiving antenna (41) both of which are circularly polarized in opposite hand senses whereby very little of a transmitted electromagnetic interrogation signal is coupled to the interrogation receiving antenna (41) and reflections from nearby surfaces are transparent, significantly improving system performance. Interrogating transmitting antenna (31) and interrogating receiving antenna (41) are cavity-backed, crossed-dipole-fed antennas producing a substantially hemispherical radiation pattern. Transponder (11) is mounted together with a dipole antenna (50) on a tag (13) carried on each article to be identified. Dipole antenna (50) includes two substantially paddle-shaped radiating members (52,53) formed upon a substrate (54), each paddle-shaped radiating member (52, 53) having an end centrally disposed on substrate (54) terminating at an angle whereby the impedance of dipole antenna (50) substantially matches the impedance of the transponder (12) in electrical connection therewith.
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Citations
12 Claims
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1. In a system for article surveillance and identification, an antenna system comprising:
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interrogating transmitting antenna means for radiating an electromagnetic interrogation signal at a center frequency and having an elliptical polarization in a first-handed direction; transponder antenna means for receiving said electromagnetic interrogation signal and reradiating a modified electromagnetic interrogation signal having a linear polarization; and
,interrogating receiving antenna means for receiving said modified electromagnetic interrogation signal at substantially said center frequency and having an elliptical polarization in a direction opposite to that of said first-handed direction. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A transponder interrogator antenna system for article surveillance and identification comprising:
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interrogating transmitting antenna means for radiating an electromagnetic interrogation signal at a preselected, instantaneous center frequency and having an elliptical polarization in a first-handed direction; and
,interrogating receiving antenna means for receiving a modified electromagnetic interrogation signal at substantially said preselected, instantaneous center frequency and having an elliptical polarization in a direction opposite to that of said first-handed direction. - View Dependent Claims (9, 10, 11)
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12. A transponder antenna system for article surveillance and identification comprising:
transponder antenna means for receiving an electromagnetic interrogation signal at a preselected frequency and reradiating a modified electromagnetic interrogation signal at substantially said preselected frequency and having a linear polarization, said transponder antenna means including a dipole antenna having two substantially paddle-shaped radiating members formed upon a substrate, each paddle-shaped radiating member having an end centrally disposed on said substrate terminating at an angle whereby the impedance of said dipole antenna substantially matches the impedance of the transponder circuit in electrical connection therewith.
Specification