METHOD AND APPARATUS FOR
DETECTING AN RFID TAG SIGNAL
 Inventor: Frederick Arnold Nylander, Morgan Hill, Calif.
 Assignee: Motorola, Inc., Schaumburg, 111.
 Appl. No.: 08/844,123  Filed: Apr. 18, 1997
 Int. CI. II01Q 11/12
 U.S. CI 343/742; 343/867; 343/866;
 Field of Search 343/742, 741,
343/867, 866, 853; 340/572; H01Q 11/12,
 References Cited
U.S. PATENT DOCUMENTS
5,126,749 6/1992 Kaltner 343/742
5,142,292 8/1992 Chang 343/742
Primary Examiner—Robert H. Kim
Assistant Examiner—Layla G. Lauchman
Attorney, Agent, or Firm—Terri S. Hughes
An antenna array for detecting a coded radio frequency identification (RFID) tag signal generated by a tag during passage of the tag through a detection volume, or portal. The array comprises at least first and second antennas disposed at different positions around the periphery of the detection volume, and circuitry, having inputs connected to receive the respective output signals from the first and second antennas and an output connected to a signal receiver for decoding the detected signal. The circuitry provides an output signal including the respective output signals of the first and second antennas, and the sum of the output signals of the first and second antennas. Preferably, the output signal of the circuitry additionally includes the inverse of the output signal of the second antenna, and the sum of the output signal of the first antenna and the inverse of the output signal of the second antenna.
22 Claims, 6 Drawing Sheets