05594448 is referenced by 131 patents and cites 6 patents.

A balanced receive antenna circuit configuration determines an accurate position of a transponder within the antenna field pattern of the reader antenna. The balanced receive antenna configuration consists of two antennas physically rotated 90 degrees relative to one another, disposed concentrically on top of one another. Furthermore, each receive antenna consists of two coils located a predetermined distance apart. The optimum distance separating the coils is determined by trading off zero position detection with the transponder detection range. A third receive reference antenna is concentrically disposed, sharing the same horizontal plane with the balanced antenna coilsets. The transmitter antenna is disposed separately from the receive antennas. In operation, initially the transmitter antenna sends a power burst signal for a predetermined duration to charge up the transponder to the maximum charge possible. Then for a very brief duration, the transmitter antenna is damped to permit the receive antennas to better receive the transponder response telegram. Then simultaneously, one receive antenna receives the `X` position component and the other receiver antenna receives the `Y` position component in the form of induced phase and voltages. Depending upon which quadrant of the antenna pattern the transponder is disposed, the phase and field effect voltage of the X component and the Y component is detected. These received voltages are then narrow band filtered around a center frequency and rectified via phase information received from the reference antenna. These rectified signals are then gated for a small portion of the length of the entire response telegram, and those outputs are combined in a signal processor which outputs the exact position data information.

Title
Highly accurate RF-ID positioning system
Application Number
141444
Publication Number
5594448
Application Date
December 15, 1994
Publication Date
January 14, 1997
Inventor
Loek d Hont
Almelo
NL
Agent
Richard L Donaldson
James C Kesterson
Rebecca A Mapstone
Assignee
Texas Instruments Incorporated
TX, US
IPC
G01S 13/74
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