RFID Foldable Antenna

Abstract

To provide an effective RFID antenna adaptable to constraints imposed by the environment in which the antenna is used.SOLUTION: An RFID antenna has two flexible elongated conductive transmission lines with coplanar RFID energy radiation perturbations distributed along the transmission lines. The transmission lines and perturbations are folded between both ends of the transmission lines, so that the transmission lines of one fold overlie and are adjacent to the transmission lines of the other fold and an electrically insulating layer disposed between lengths of the transmission lines on one side of the fold.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an RFID antenna. [Background technology]

[0002] US Patent No. 5,399,633 discloses a high performance RFID antenna that includes a serpentine transmission or feed line and dipoles or stubs spaced along the length of the transmission line to form perturbations. The transmission line and dipoles are housed between two sheets of foam board to create a planar, relatively rigid assembly. The patented antenna is capable of providing item level servicing.

[0003] There are occasions when an RFID antenna is required for reasons of space, protection, or aesthetics to be built into a cabinet, a portal such as a doorway, a wall, or other space. Many of these situations do not easily accommodate a rigid, relatively long antenna. Thus, there is a need for an effective RFID antenna that can adapt to the constraints imposed by the environment in which it will be used. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 8,058,998 Summary of the Invention [Problem to be solved by the invention]

[0005] To provide an effective RFID antenna that can adapt to the constraints imposed by the environment in which the antenna is used. [Means for solving the problem]

[0006] It has become apparent that an antenna such as that disclosed in the aforementioned patents can essentially fold itself or, if done properly, be distorted from a single plane with no loss of performance and in some cases even improved results. To achieve this versatility, the transmission lines and dipoles of the antenna are preferably mounted on a flexible film, free of the constraints imposed when mounted on a rigid body. For maximum performance, the stubs or radiators of one folded layer should not overlap or cross the stubs of another folded layer.

[0007] Folding, if done properly, can improve performance and not degrade it. For example, folding is done to best ensure that all tags are read within and constrained to the desired read zone. This folding also reduces the number of antennas required to read all tags, thus potentially providing a more efficient solution. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic plan view of a nominal three foot antenna constructed in accordance with the present invention. [Diagram 2] FIG. 2 is a schematic plan view of a nominal 5 foot antenna constructed in accordance with the present invention. [Diagram 3] FIG. 3 is a schematic plan view of a nominal 7 foot antenna constructed in accordance with the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the antenna shown in FIGS. [Diagram 5] FIG. 5 is an example of a preferred folding method for an antenna such as the 7 foot antenna of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The RFID antennas 10a, 10b, 10c of the present invention have parallel feed lines or transmission lines 11 arranged in a symmetrical meandering curved pattern with small spacing 12 about an axis 13. The transmission lines 11 can be thin foils of aluminum or other conductive metal. Dipoles or stubs 14, located where the transmission lines cross the axis 13, are electrically connected to the respective feed lines 11 and can be of the same conductive material as the feed lines. The feed lines 11 and the dipoles or radiators 14 are preferably coplanar. As shown, the dipoles are perpendicular to the local direction of their respective feed lines, and are preferably at an angle of +45 degrees or -45 degrees to the axis. One end of each feed line 11 is independently connected to either the inner or outer conductor of a coaxial cable. The antenna features diversity of both electric field polarization and beam direction with relatively uniform signal strength radiated from each dipole radiator 14.

[0010] Figure 4 shows a typical cross-section of the antenna of Figures 1-3. A flexible Mylar® base 16, for example 0.1 mm thick, carries a thin foil of 0.1 mm aluminium which forms the feedline 11 and dipole 14. The aluminium foil is secured to the Mylar® base 16 with double sided tape 17. The Mylar® film or sheet 17, like the aluminium foil, is elastically flexible in its plane, and like the adhesive tape 17, forms a coplanar feedline 11 and stub 14.

[0011] The antenna 10a, 10b, 10c supported by layers of Mylar® film can be folded on itself, front to front or back to back, to form a sandwich preferably 1 / 2 inch thick or greater, without damage to the Mylar® film, transmission lines, stubs, or tapes. Thus, the fold radius should be no less than 1 / 4 inch. To prevent bonding between the feedlines 11 of the folded layers, a layer of plastic foam, e.g., 0.5 inch thick, can be placed between the layers.

[0012] For the antenna to work properly, the base Mylar® and transmission line composite must be folded so that the dipoles 14 or perturbations on one layer do not overlap with the dipoles or perturbations on another layer. Figure 5 shows this condition, which improves the diversity of the radiation.

[0013] The dipoles or stubs 14 mentioned above are directly connected to the feed line 11. These stubs 14 represent perturbations to the feed line 11 and radiate RFID energy. The equivalent perturbations are similarly coplanar with the feed line 11 and can be in the form of abrupt changes in the path or shape of the planar feed line, such as notches cut into the feed line, or abrupt changes in the electrical properties of the feed line (e.g., width and spacing of the coplanar feed lines). The radiating stubs 14 or their equivalents do not need to be in electrical contact with the feed line. Slot, loop, or patch radiators can be used, which can be functionally capacitively or inductively coupled to each strip of the feed line. The perturbations or stubs 14 can be spaced approximately (i.e., ±15%) wavelength apart.

[0014] It will be apparent that the present disclosure is an example and that various modifications can be made by adding, modifying, or deleting details without departing from the fair scope of the teachings contained herein. Accordingly, the invention is not limited to the particular details of this disclosure except to the extent that the following claims are necessarily limited thereto. [Explanation of symbols]

[0015] 10a, 10b, 10c RFID antenna 11 Transmission Lines 12 intervals 13 Axis 14 Stub 16 Mylar® based 17 Tape

Claims

1. 1. An RFID antenna having two flexible, elongated, electrically conductive transmission lines and coplanar RFID energy radiating perturbations distributed along the transmission lines, the transmission lines and perturbations folded between opposite ends of the transmission lines such that the transmission lines overlap in one fold and are adjacent the transmission lines in another fold and an electrically insulating layer disposed between the transmission lines in the other fold and the lengths of the transmission lines on either side of the fold.

2. The antenna of claim 1 , wherein the transmission line is in a meandering pattern.

3. The antenna of claim 1 , wherein the perturbations are positioned such that the perturbations of one fold do not overlap with the perturbations of another fold.

4. The antenna of claim 1 , wherein the perturbation is a stub extending from the transmission line.

5. 1. An RFID antenna comprising a pair of elongated, substantially parallel, spaced apart feedlines and radiation-generating perturbations spaced along said feedlines, said feedlines and perturbations being in a common plane, said feedlines comprising flat metallic conductors, said feedlines being flexible and supported on a flexible layer of non-conductive material, said feedlines being capable of being warped in a warp curve from a single plane without damaging said flexible layer, whereby layers of said feedlines can be within a distance of 1-1 / 2 inches or less of each other adjacent said warp curves.

6. The RFID antenna of claim 5 , wherein the feed line is in a serpentine pattern.

7. The RFID antenna of claim 5 , wherein the perturbation is a stub extending laterally from the feed line.

8. The RFID antenna of claim 7 , wherein each of the stubs is connected to a feed line.

9. The RFID antenna of claim 5 , wherein the flexible layer is a plastic film.

10. The RFID antenna of claim 7 , wherein the plastic is Mylar®.

11. 10. The RFID antenna of claim 9, wherein the Mylar® has a nominal thickness of 0.10 mm.

12. 6. The RFID antenna of claim 5, wherein the metal conductor is aluminum with a thickness of 0.1 mm.

13. An RFID antenna having an elongated parallel transmission line and a radiation emitting perturbation distributed along said transmission line, said transmission line and perturbation being coplanar and resiliently flexible without a rigid support structure, said transmission line and perturbation being capable of being bent at small radii of as little as ¼ inch out of plane without damage to said transmission line and perturbation to conform to a more rigid structure.

14. 14. The RFID antenna of claim 13, wherein the RFID antenna is foldable such that the transmission line and the perturbation can be folded onto itself without damage into a sandwich-like structure having an interlayer dimension between lengths of the transmission line as small as ½ inch.

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