Phased array antenna for radio frequency identification

• US 6,127,981 A
• Filed: 07/23/1997
• Issued: 10/03/2000
• Est. Priority Date: 10/13/1995
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Greene, Edward E., Pritchett, Don Michael, Milicic, Matthew J. Jr.
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US08/899,166
• Time in Patent Office: 1,168 Days
• Field of Search: 343/711, 343/814-816, 343/821, 343/795, 343/853, 340/572
• US Class Current: 343/711
• CPC Class Codes: H01Q 1/3225 Cooperation with the rails or the road
• CPC Class Codes: H01Q 19/10 using reflecting surfaces
• CPC Class Codes: H01Q 19/30 the primary active element being centre-fed and substantially straight, e.g. Yagi antenna
• CPC Class Codes: H01Q 21/0006 Particular feeding systems
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H01Q 9/26 with folded element or elements, the folded parts being spaced apart a small fraction of operating wavelength resonant loop antennas H01Q7/00

Abstract

A multi-element, H plane, phase, dipole array antenna has a high gain over a wide angle in azimuth and over a controlled sector in elevation. Two printed wiring boards feed and physically support the dipole antenna elements. The phase and spacing of the dipole elements establish the radiation elevation angle, and a planar metallic reflector, spaced on the order of a half wavelength of the RF signal from the dipole array, interacts with the dipole-element pattern, to provide the wide angle azimuth gain.

Claims

1. A radio-frequency interrogation method for reading a transponder tag on an object moving with respect to a surface as the transponder tag moves along a path past a fixed position adjacent said path, including the steps of:

stationing at said fixed position a phase array antenna comprised of a plurality of dipole radiating elements disposed adjacent said path in a plane parallel to said surface; and

energizing said antenna array to irradiate said transponder tag with a radio-frequency beam whose principal lobe axis in an elevation direction is directed from said fixed position so said beam intersects said path and whose gain in an azimuth direction along said path on either side of the principal lobe axis in an elevation direction is greater than the gain along said principal lobe axis in azimuth, so that the coupling between said tag and said antenna is extended in azimuth as said tag approaches toward and recedes from said antenna along said path, and said coupling is maintained when said tag intersects said principal lobe axis.

2. A radio frequency interrogation method as in claim 1 wherein said fixed position is adjacent said path, said moving object is a railroad car moving on parallel tracks, and said dipole elements lie in a plane parallel to and below the plane of a tracks.