Antenna array in an RFID system

• US 6,184,841 B1
• Filed: 12/31/1996
• Issued: 02/06/2001
• Est. Priority Date: 12/31/1996
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Wu, You-Sun, Sweetman, Eric, Shober, R. Anthony
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): PHAN, THO GIA
• Application Number:
  US08/775,217
• Time in Patent Office: 1,498 Days
• Field of Search: 343/700.MS, 343/813, 343/814, 343/844, 343/853, 343/850, 343/858, 343/860, 343/778, 342/42, 342/44, 342/51, 455/41, 455/49, 455/54
• US Class Current: 343/853
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 21/08 the units being spaced along or adjacent to a rectilinear path waveguide fed H01Q21/0037
• CPC Class Codes: H01Q 9/18 Vertical disposition of the antenna

Abstract

In accordance with the present invention, a general antenna system is disclosed suitable for applications in which an RFID Tag passes by an Interrogator. We then disclose a specific antenna design that uses a single planar antenna for transmit and a multi-element planar antenna array for receive. The multi-element planar antenna array is spaced such that each of the planar elements is four inches apart, center-to-center, thus defining a narrow 30° receive beamwidth in the horizontal plane. The vertical receive bandwidth is much greater than 30°, facilitating the Interrogator receiving signals at a variety of elevations. Furthermore, a multi-way microstrip combiner is used to sum the signals received from each of the planar antennas. To block interference from the transmit antenna and to improve receive sensitivity, this multi-way microstrip combiner is shielded using, in one embodiment, copper tape along its edges. In a specific embodiment, a four element receive antenna design is disclosed.

Claims

1. A radio frequency identification system, comprising:

an interrogator having a transmit antenna and a receive antenna,

an antenna gain of said transmit antenna being less than an antenna gain of said receive antenna, and

a vertical beamwidth of said receive antenna being greater than a horizontal beamwidth of said receive antenna.

2. The radio frequency identification system of claim 1, wherein said receive antenna comprises N planar antenna elements configured in a 1×

N array, where N is one of 2, 4, and 8.

3. The radio frequency identification system of claim 1, wherein said transmit antenna is a single planar antenna.

4. The radio frequency identification system of claim 1, wherein said transmit and receive antennas are separated by at least two inches.

5. The radio frequency identification system of claim 1, wherein said transmit and receive antennas are linearly polarized.

6. The radio frequency identification system of claim 5, wherein the receive antenna comprises N planar antenna elements, each separated by at least two inches.

7. The radio frequency identification system of claim 5, wherein the receive antenna comprises N planar antenna elements and the signals from said N planar antenna elements are combined using an in-phase power combiner.

8. The radio frequency identification system of claim 7, wherein in-phase power combiner is electrically shielded along its edges.

9. The radio frequency identification system of claim 7, wherein the receive antenna comprises four planar elements, and

said in-phase power combiner comprises three binary combiners in cascade.

10. The radio frequency identification system of claim 9, wherein said four planar antenna elements are mounted back-to-back with said in-phase power combiner.