WO2000021031A1

WO2000021031A1 - Rfid tag having dipole over ground plane antenna

Info

Publication number: WO2000021031A1
Application number: PCT/US1999/023036
Authority: WO
Inventors: Michael John Brady; Dah-Weih Duan; Venkata S. R. Kodukula; Paul Andrew Moskowitz; Philip Murphy
Original assignee: Intermec Ip Corp.
Priority date: 1998-10-06
Filing date: 1999-10-04
Publication date: 2000-04-13

Abstract

An RFID tag (100) having a dipole over ground plane (DOG) antenna is disclosed. The DOG antenna structure allows the RFID tag (100) to be placed on metal or RF absorbing surfaces and to be read over increased ranges. The RFID tag includes an RF transponder (102) for communicating with an RFID system. A base plate (120) which may be attached to a metal or RF absorbing surface forms a conducting ground plane. A support (118) is attached to the base plate and holds the RF transponder (102) so that its dipole is spaced at a distance from the conducting ground plane.

Description

RFID TAG HAVING DIPOLE OVER GROUND PLANE ANTENNA

Cross-Reference to Related Applications The present application claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application Nos. 60/073,099, filed January 30, 1998; 60/076,363, filed February 27, 1998; and 60/078,292, filed March 17, 1998 and U.S. Provisional Application to Brady et al. (Express Mail Label No. EL 025 200 246 US), filed October 6, 1998. Said U.S. Provisional Application Nos. 60/073,099, 60/076,363, 60/078,292 and Provisional Application to Brady et al. (Express Mail Label No. EL 025 200 246 US) are herein incorporated by reference in their entirety.

Incorporation by Reference The following US Patents and Patent Applications are hereby incorporated herein by reference in their entirety:

U.S. Patents

Patent No. Issue Date Filinα Date Attorney Docket

No.

5,521 ,601 05/28/96 04/21/95 YO995-0088

5,528,222 06/18/96 09/09/94 YO994-180

5,538,803 07/23/96 11/23/94 YO994-0073

5,550,547 08/27/96 09/12/94 YO994-185

5,552,778 09/03/96 11/23/94 YO994-0232

5,554,974 09/10/96 11/23/94 YO994-0071

5,563,583 10/08/96 11/23/94 YO994-070

5,565,847 10/15/96 11/23/94 YO994-0072

5,606,323 02/25/97 08/31/95 YO995-157

5,635,693 06/03/97 02/02/95 YO994-0215

5,673,037 09/30/97 09/09/94 YO994-184

5,680,106 10/21/97 10/27/95 YO995-0219

5,682,143 10/28/97 09/09/94 YO994-170

5,729,201 03/17/98 06/29/95 YO995-109 Patent No. Issue Date Filinα Date Attorney Docket No.

5,729,697 03/17/98 04/24/95 YO995-076

5,736,929 04/07/98 06/07/96 YO996-085

5,777,561 07/07/98 09/30/96 Y0996-178

U.S. Nonprovisional Patent Applications

Application No. Filinα Date Attorney Docket No.

08/681 ,741 07/29/96 YO996-037

08/660,249 06/07/96 YO996-084 (allowed 4-28-98)

08/621 ,784 03/25/96 YO996-031

08/626,820 04/03/96 Y0995-158

08/646,539 05/08/96 YO996-068

08/681 ,741 07/29/96 YO996-037

08/694,606 08/09/96 Y0995-218

08/790,639 01/29/97 YO997-024

08/790,640 01/29/97 YO997-023

08/733,684 10/17/96 YO996-195

08/862,149 05/23/97 YO997-116

08/862,912 05/23/97 YO997-115

08/862,913 05/23/97 YO997-114

08/909,719 08/12/97 YO995-109B (allowed) 08/935,989 10/23/97 YO997-310

U.S. Provisional Patent Applications

Application No. Filinα Date Attorney Docket No.

60/073,102 01/30/98 YO897-0028P1

60/074,605 02/13/98 YO897-0259P1

60/077,879 03/13/98 YO997-0038P1

60/078,287 03/17/98 YO897-0661 P1 Application No. Filinα Date Attorney Docket No. 60/078,304 03/17/98 YO897-0662P1 60/091 ,350 07/01/98 YO897-0259P2 60/093,088 07/16/98 38384P1

The following further documents are also incorporated herein by reference in their entirety:

IBM Technical Disclosure Bulletin IBM Technical Disclosure Bulletin: Vol. 38 No. 08, August 1995, page 17, "Multifunction Credit Card Package," by Brady, Moskowitz, and Murphy (published anonymously).

Literature Reference D. Friedman, H. Heinrich, D. Duan, "A low-power CMOS integrated circuit for field-powered radio frequency identification (RFID) tags," 1997 Digest of Technical Papers of the IEEE International Solid-State Circuits Conference (ISSCC), San Francisco, CA, February 1997.

PCT Published International Applications

Application No. Filinα Date Attorney Docket No.

PCT/GB96/00061 01/15/96 UK 9-94-066 PCT

PCT/EP95/03703 10/20/95 Y0994-242 PCT UK Published Application

Application No. Filinα Date Attorney Docket No. 9710025.9 05/19/97 YO9-96-084

Field of the Invention The present invention relates generally to radio frequency identification (RFID) systems, and more specifically to RFID tags having a dipole over ground plane (DOG) antenna structure for use in RFID systems. Background of the Invention

Radio Frequency Identification (RFID) is becoming an important identification technology in applications such as inventory management, security access, personnel identification, factory automation, automotive toll debiting, and vehicle identification to name just a few. RFID systems utilize an RFID transmitter-receiver unit (usually referred to as a base station or interrogator) to query an RFID transponder or tag which may be located at a distance from the transmitter-receiver unit. The RFID tag detects the interrogating signal and transmits a response signal containing encoded data back to the receiver. RFID systems provide identification functions not found in identification technologies such as optical indicia (e.g., bar code) recognition systems. For example, RFID systems may employ RFID tags containing read/write memory of several kilobytes or more. The RFID tags may be readable at a distance and do not require direct line-of-sight view by the reading apparatus (e.g., base station or interrogator). Further, several such RFID tags may be read by the RFID system at one time.

Often it is desirable to place an RFID transponder on a metal or RF absorbing surface such as an automobile, truck, trailer, cargo container, steel or aluminum warehouse pallet, etc. In such applications, the transponder may suffer limitations in range due to the effect of the metal surface on the impedance of its antenna. Further, conventional transponders may be damaged by harsh outdoor or warehouse environments. Consequently, it would be desirable to develop an RFID tag using a dipole over ground plane antenna wherein the tag may be placed on metal or RF absorbing surfaces while providing increased range. Summary of the Invention

Accordingly, the present invention provides a novel RFID tag having a dipole over ground plane (DOG) antenna structure. The DOG structure allows the RFID tag to be placed on metal or RF absorbing surfaces and to be read over increased ranges. The RFID tag includes an RF transponder configured to communicate with an RFID system. A base plate which may be attached to a metal or RF absorbing surface forms a conducting ground plane. The RF transponder includes a dipole which is held at a distance from the conducting ground plane by a support attached to the base plate. The support may comprise a housing which encloses the RF transponder to protect it from environmental contaminants.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.

Brief Description of the Drawings The numerous objects and advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:

FIG. 1 A is an isometric view of an exemplary RFID tag in accordance with an exemplary embodiment of the present invention;

FIG. 1B is a cross-sectional profile view of the RFID tag shown in FIG. 1 ;

FIG. 2A is an isometric view of an embodiment of the RFID tag wherein the support has a trapezoidal cross-section;

FIG. 2B is a cross-sectional profile view of the RFID tag shown in FIG. 2A; FIG. 3 is a cross-sectional profile view of an embodiment of the RFID tag wherein the support has an arcuate cross sectional profile; FIG. 4A is an isometric view of the dipole and ground plane of the RFID tag of the present invention illustrating methods of tuning the impedance of the antenna;

FIG. 4B is a side elevational view of the dipole shown in FIG. 3A; FIG. 4C is a top plan view of the tuning snub of the dipole shown in FIG.

3A; and

FIG. 5 is a view illustrating an RFID system employing an RFID tag having a dipole over ground plane (DOG) antenna in accordance with the present invention. Detailed Description of the Invention

Reference will now be made in detail to the presently preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Referring now to FIGS. 1A and 1 B, an RFID tag in accordance with an exemplary embodiment of the present invention is shown. The RFID tag 100 has a dipole over ground plane (DOG) antenna structure. The DOG antenna structure allows the RFID tag 100 to be placed on metal or RF absorbing surfaces (see FIG. 5) and to be read over increased ranges compared to an RFID tag employing a tuned dipole antenna. The RFID tag 100 includes an RFID transponder 102 which is configured to communicate with an RFID system via the system's base unit or a handheld interrogator (see FIG. 5). The RFID transponder 102 preferably includes a packaged RFID integrated circuit (RFID IC) 104 including RF modulator circuits, logic circuits, and memory mounted to a substrate 106 and bonded to a dipole 108. Substrate materials include polyester, polyimide, ceramics, FR-4 epoxy, phenolic, and other dielectric materials. The packaged RFID IC 104 preferably comprises an RFID IC chip encapsulated within a plastic-molded package 110. The package 110 may be a single in-line package (SIP), dual in-line package (DIP), or preferably a flat pack (shown). Typical flat pack IC packages which may be employed by the present invention include, but are not limited to, small outline packages (SOP), miniature small outline packages (MSOP), and small outline integrated circuit (SOIC) packages. Preferably, the package 110 includes a plurality of external leads or pins 112 which are connected (as required by the IC design) to the RFID IC chip via conventional techniques (such as wire bonding or the like). For example, two of the leads 112 may connect the RFID IC chip to the dipole 108 formed on the substrate 106 (i.e., the leads 112 may be soldered to the dipole 108 using convention soldering techniques). Alternatively, the RFID IC chip may be directly mounted to the substrate 106 and bonded to the dipole 108. The RFID IC chip may be coated with an encapsulant, such as a "glob-top" epoxy, or the like and/or laminated with a laminate to protect the chip (and bonds between the dipole and chip) from damage.

The dipole 108 may be integrally formed on the substrate 106. Preferably, the dipole 108 comprises thin, typically 18 to 35 micron thick, lines formed of a conductive metal such as copper. These lines may be formed by plating, adhering or screening a thin layer of copper (or other conductive metal) onto to the substrate 106. This layer may then be etched to form the specific geometric configuration of the dipole 108 (i.e., simple dipole, folded dipole, meander dipole, etc.). An advantage of the dipole over ground plane (DOG) antenna structure is that at a suitable standoff distance (see FIG. 4A), such as about 7 percent to 11 percent of a wavelength, the radiation resistance of a resonant dipole (about 73 ohms) is reduced to a lower value (i.e., about 10 ohms). Preferably, this lower resistance value is close to the resistance of the RFID IC 104 providing a good starting point for impedance matching which may be perfected by other impedance adjustment elements (i.e., tuning stubs, loading bars, impedance matching circuits, etc.). One or more such impedance adjustment elements may be integrally formed on the substrate 106 to modify the impedance of the dipole 108. The impedance adjustment elements may be lumped circuit elements, distributed microwave circuit elements, or a parasitic element that is electromagnetically coupled to the dipole 108 (i.e., not electrically connected). For example, the dipole 108 may include a tuning stub 114 having a length and width adjusted to tune the impedance of the dipole 108. The tuning stub 114 acts as a two conductor transmission line and may be terminated either in a short-circuit or open-circuit. A short circuited stub acts as a lumped inductor while an open-circuit stub acts as a lumped capacitor. The magnitude of the reactance of the tuning stub 114 is affected by the stub's length, width, and spacing. Similarly, one or more impedance loading bars 116 may be positioned on the substrate 106 adjacent to the dipole 108 so they are electromagnetically coupled to the dipole 108 to modify its impedance.

The RF transponder 102 may be "active" meaning that the transponder 102 includes an internal transmitter for transmitting information to an interrogator or base station (not shown), or "passive" meaning that the transponder uses a modulated back scattered RF field (generated by the interrogator or base station) to provide a return signal to provide the information. The RF transponder 102 may be field powered, or alternatively, may be at least partially battery powered. Field powered transponders collect power from the RF field generated by the interrogator or base station and convert the collected power to a dc voltage which is stored in a capacitor to provide power for operating the transponder's other circuitry. Battery powered transponders typically employ coin shaped battery (not shown) mounted to the substrate 110 and electrically connected to the RFID IC 104. While a typical RF transponder has been illustrated and described herein in connection with FIG. 1 , numerous other RF transponder designs or configurations presently exist or may be developed in the future. Thus, it should be appreciated that modification or reconfiguration of the RF transponder 102 of FIG. 1 by one having ordinary skill in the art would not depart from the scope or the spirit of the present invention.

The RF transponder 102 is held by a non-conducting support 118 at a fixed distance from a base plate 120 which forms a conducting ground plane.

In this manner, the dipole 108 is suspended over and held generally parallel to the conducting ground plane. Preferably, the dipole 108 is a one half wavelength (λ) dipole radiator and is suspended approximately one tenth of a wavelength (λ) above the conductive ground plane wherein the wavelength (λ) is determined by the frequency at which the RFID system operates.

The base plate 120 which forms the ground plane may be rectangular in shape and may be attached to a metal or RF absorbing surface (see FIG. 5) via as fastener 122 such as an adhesive, double-sided tape (shown), rivets or bolts (via holes 124), hook and loop fastener material, or the like. When attached to the metal or RF absorbing surface, the bottom of the base plate 120 abuts the surface so that the RF transponder 102 is held away from the surface by the support 118. Preferably, the base plate 120 is made of a metal (i.e., aluminum, steel, brass, titanium, copper, etc) or a metallized material (i.e., a metallized plastic, mesh, screen, etc). The base plate 120 may have dimensions (i.e., length and width) on the order of one half of a wavelength (λ) wherein the wavelength (λ) is determined by the frequency at which the RFID system operates.

The RF transponder 102 may be attached to a surface within the support 118 via a fastener such as an adhesive, double-sided tape, rivets, "snap-on" molded plastic tabs, or the like. The support 118 may be attached to the base plate 120 (via a fastener such as an adhesive, rivets, bolts, etc.) and sealed to prevent environmental contaminants from reaching the RF transponder 102. Preferably, the support 118 is made of a non-conducting material such as polypropylene plastic.

As shown in FIG. 1B, the support 118 may comprise a hollow shell having a rectangular cross-section. The support 118 may include an outer wall 126, first and second side walls 128 & 130, first and second end walls 132 (FIG. 1 A) & 134 and a generally rectangular open end 136 opposite the outer wall 126. Edges 138 of the first and second side walls 128 & 130 and first and second end walls 132 (FIG. 1A) & 134 opposite the outer wall 126 are attached and sealed to the base plate 120 via an adhesive, sealant, or the like. Preferably, the RF transponder 102 is placed within the support 118 via the open end 136 and attached to the inner surface of the outer wall 126 so that it is held generally parallel to the base plate 120 and conducting ground plane. The first and second side walls 128 & 130 and first and second end walls 132 (FIG. 1 A) & 134 space the outer wall 126 and RF transponder 102 attached thereto from the base plate 120 and ground plane. Further, the RF transponder 102 is preferably sealed within the support 118 when the support 118 is attached to the base plate 120 so that the RF transponder 102 is protected from environmental contaminants.

Referring now to FIGS. 2A and 2B, an RFID tag having a support in accordance with a second exemplary embodiment of the present invention is shown. The support 202 of this embodiment of the RFID tag 200 may comprise a hollow shell having a generally trapezoidal cross-section and including an outer wall 204 parallel to the base plate 206, opposed first and second trapezoidal end walls 208 & 210 and first and second side walls 212 & 214 extending at generally equal obtuse angles from outer wall 204. Preferably, the side and end walls 208, 210, 212 & 214 form a generally rectangular open end 216 opposite the outer wall 204 wherein the edges 218 of the first and second side walls 212 & 214 and first and second end walls 208 & 210 opposite the outer wall 204 are attached and sealed to the base plate 206 via an adhesive, sealant, or the like. As with the generally rectangular support 118 (FIGS. 1A and 1 B), the RF transponder 220 (which may be constructed similarly to the RF transponder 102 shown in FIGS. 1A and 1B) is placed within the trapezoidal support 202 via the open end 216 and attached to the inner surface of the outer wall 204 so that it is held generally parallel to the base plate 206 and conducting ground plane. The first and second side walls 212 & 214 and first and second end 208 & 210 walls space the outer wall 204 and RF transponder 220 attached thereto from the base plate 206 and ground plane. Further, the RF transponder 220 is preferably sealed within the support 202 when the support 202 is attached to the base plate 206 so that the RF transponder 220 is protected from environmental contaminants.

Referring now to FIG. 3, an RFID tag having a support in accordance with an alternative embodiment of the present invention is shown. The support 302 of this embodiment of the RFID tag 300 includes an outer wall 304 having an arcuate cross section and first and second semi-circular end walls 306. Edges 308 of the outer wall 304 and the first and second end walls 306 are attached and sealed to the base plate 310 via an adhesive, sealant, or the like. Preferably, the RF transponder 312 (which may be constructed similarly to the RF transponder 102 shown in FIGS. 1A and 1 B) is placed within the support 302 and attached to the inner surface of the outer wall 304 so that it is held generally parallel to the base plate 310 and conducting ground plane. Preferably, the curvature of the outer wall 304 causes the RF transponder 312 to be held at a fixed distance from the base plate 310 and ground plane. The RF transponder 312 is preferably sealed within the support 302 when the support 302 is attached to the base plate 310 so that the RF transponder 312 is protected from environmental contaminants.

In view of FIGS 1A through 3, it should now be appreciated that supports may be provided by one of ordinary skill in the art which have wide variety of cross-sections. For example, supports may be provided which have generally triangular cross-sections, generally polygonal cross-sections, or curvilinear cross-sections. Supports having such cross-sections are anticipated by and would not depart from the scope or the spirit of the present invention

Referring now to FIGS 4A, 4B and 4C, methods of adjusting or matching the impedance of RFID tags using dipole over ground plane (DOG) antennas are illustrated. As shown in FIG. 4A, the dipole 402 of the RFID tag 400 may be mounted (as described in FIGS. 1A through 3) at a distance ("H") from a conducting ground plane 404. Preferably, the ground plane 404 comprises a flat base plate 406 having a length ("L_g") and a width ("W_g"). As shown in FIG. 4B, the dipole 402 may have a length ("L") and a width ("W"). The dipole 402 shown is a simple dipole having two elements 408 & 410. One or more tuning stubs 412 may be formed in either or both elements 408 & 410. Each tuning stub 412 comprises parallel stub lines 414 & 416 extending perpendicularly from a dipole element 408 & 410. Preferably, the stub lines 414 & 416 are generally parallel to the conducting ground plane 404. Each tuning stub 412 acts as a two conductor transmission line and may be terminated either in a short-circuit or open-circuit (a short-circuit is shown). A short circuited stub acts as a lumped inductor while an open-circuit stub acts as a lumped capacitor. As shown in FIG. 4C, the tuning stub 412 may have a stub line length ("L_s"), a sub line width ("W_s"), and an edge-to-edge distance or space between stub lines ("S_s"). The tuning stub 412 may be positioned along the element 408 & 410 at a distance ("X_s") from the center of the dipole 418. One or more impedance loading bars (see FIG. 1 ) may be positioned adjacent to the antenna 402. Use of tuning stubs and impedance loading bars to adjust the impedance of an antenna is described in detail in U.S. Patent Application Serial No. 08/790,639 to Duan, et al. filed January 29, 1997 which is herein incorporated by reference in its entirety.

Preferably, the impedance of the antenna 402 may be adjusted depending on the frequency of the RFID system it is to be used with by modifying at least one of the width of the dipole ("W"), the length of the dipole antenna ("L"), the distance between the dipole and the conducting ground plane ("H"), and/or the size of the conducting ground plane (i.e., the length ("L_g") and width ("W_g") of the base plate 404). Wherein the antenna 402 includes one or more tuning stubs 412, the impedance of the antenna may further be adjusted by modifying at least one of the width of the tuning stub (e.g., stub line width ("W_s")), the length of the tuning stub (e.g., stub line length ("L_s")), the distance of the tuning stub from the center of the dipole ("X_s"), and/or the edge to edge space between the stub lines ("S_s"). For example, an advantage of the dipole over ground plane (DOG) antenna structure is that at a suitable distance ("H"), such as about 7 percent to 11 percent of a wavelength, the radiation resistance of a resonant dipole (about 73 ohms) is reduced to a lower value (i.e., 10 ohms). Preferably, this lower resistance value is close to the resistance of the RFID IC (see FIGS. 1A through 3) providing a good starting point for impedance matching which may be perfected by other impedance adjustment elements (i.e., tuning stubs, loading bars, impedance matching circuits, etc.). In an exemplary embodiment, an RFID tag having a dipole over ground plane (DOG) antenna structure may be configured for use in an RFID system which operates at a frequency of, for example, 2.45 GHz. For this embodiment, the antenna of the RF transponder may comprise a dipole having a tuning stub which is etched on a standard printed circuit board mounted by an adhesive to the inside of the RFID tag's support. The RF transponder's circuit chip is enclosed in a plastic package (i.e., a small outline integrated circuit (SOIC), miniature small outline package (MSOP), etc.) which is mounted to the substrate and soldered to the antenna. Preferably, the antenna is held at a distance ("H") of approximately 10 millimeters (mm) above the base plate and has a length ("L") of less than about 50 mm and a width ("W") of approximately 0.5 mm. The tuning stub is positioned at a distance from the center of the dipole ("Xs") of approximately 10 mm and has a width ("Ws") of about 0.25 mm, a length ("Ls") of about 5 mm, and a edge-to-edge space between stub lines ("Ss") of about 0.5 mm. The base plate of the RFID tag is approximately 54 to 55 mm in width ("Wg") by 85 to 86 mm in length ("Lg"). For this configuration, the range of the RFID tag has been measured to be approximately 1.4 meters (m) which represents an increase of approximately 75 percent over the range of a comparable tuned dipole.

Referring now to FIG. 5, an RFID system employing an RFID tag having a dipole over ground plane (DOG) antenna structure in accordance the present invention is shown. The RFID system 500 includes an RF transmitter-receiver unit (typically referred to as a base station or interrogator) 502 to query the RFID tag 504 located at a distance from the unit. The interrogator 502 may be fixedly located (a central base station), hand-held (i.e., a hand-held portable data collection terminal or computer), or mounted to a vehicle (i.e., a forklift, delivery truck, etc.). Preferably, the interrogator 502 includes an RF transmitter, an RF receiver and an antenna. The RFID tag 504 receives the interrogating signal and transmits a response signal comprising encoded data back to the interrogator's receiver. The data encoded in the response signal may be as simple as 1-bit (the response indicates that the tag 504 is present or absent) or the data may be a serial stream providing a substantial amount of data to the interrogator 502. Operating frequencies of such systems typically range from 13 MHz to 6 GHZ.

Preferably, the RFID tag 504 may be placed on a metal or RF absorbing surface 506 without suffering significant degradation of its operating range. For example, the RFID tag 504 may be attached to the metal surface 506 of an object 508 such as an automobile, truck, trailer, cargo container, steel or aluminum warehouse pallet, etc. using a fastener such as an adhesive, double sided tape, screws, rivets, bolts, or the like. The RFID tag's RF transponder may be encoded with information relating to the goods or products 510 held by the object 508. This information may, for example, be transmitted and written to the RF transponder's memory via the interrogator 502 and may include inventory information such as serial number, amount of goods, destination of goods, shipping instructions, etc. The interrogator 502 may query the RFID tag

504 to acquire this information when needed by users of the RFID system 500.

Various modifications may be made in and to the above described embodiments without departing from the spirit and scope of the invention. For example, various modifications and changes may be made in the configuration of the RF transponder such as reconfiguration of the antenna geometry, battery arrangement, circuit chip construction, substrate material and geometry, and the like. Further, use of the RFID tag is directed to a wide variety of applications including, but not limited to, airline baggage (i.e., luggage, freight, and mail), postal service, manufacturing, inventory control, personnel security, and the like.

It is believed that the RFID tag of the present invention and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.

Claims

ClaimsWhat is claimed is:

1. A RFID tag, comprising: an RF transponder configured to communicate with an RFID system, said RF transponder including a dipole; a base plate forming a conducting ground plane; and a support attached to said base plate for retaining said RFID transponder so that the dipole is held at a distance from the conducting ground plane.

2. The RFID tag of claim 1 , wherein said RF transponder further comprises: a substrate mounted to said support and carrying the dipole; and an RFID IC mounted to the substrate and coupled to the dipole.

3. The RFID tag of claim 2, wherein the RFID IC is packaged within a package mounted to the substrate and wherein the package interconnects the RFID IC to the dipole.

4. The RFID tag of claim 3, wherein the package is a small outline (SO) package.

5. The RFID tag of claim 1 , wherein the dipole has a simple dipole structure.

6. The RFID tag of claim 1 , wherein the dipole has a folded dipole structure.

7. The RFID tag of claim 1 , wherein the dipole has a meander dipole structure.

8. The RFID tag of claim 1 , wherein the impedance of the antenna is adjusted by modifying at least one of the width of the dipole, the length of the dipole, the distance between the dipole and the conducting ground plane, the size of the conducting ground plane.

9. The RFID tag of claim 1 , wherein the dipole includes a tuning stub comprising parallel stub lines.

10. The RFID tag of claim 9, wherein the impedance of the antenna may be adjusted by modifying at least one of the width of the tuning stub, the length of the tuning stub, the distance of the tuning stub from the center of the dipole, and the edge to edge space between the stub lines.

11. The RFID tag of claim 1 , wherein said base plate is made of metal.

12. The RFID tag of claim 11 , wherein the metal is selected from the group consisting of aluminum, steel, brass, titanium, and copper.

13. The RFID tag of claim 1 , wherein said base plate is made of a metallized material.

14. The RFID tag of claim 13, wherein the metallized material is a metallized plastic.

15. The RFID tag of claim 13, wherein the metallized material is a metallized mesh.

16. The RFID tag of claim 1 , wherein a dimension of said base plate is approximately one half wavelength.

17. The RFID tag of claim 1 , wherein said support holds said RF transponder above the conducting ground plane at a distance of approximately 7 percent to 11 percent of a wavelength.

18. The RFID tag of claim 1 , wherein said support has a generally rectangular cross-section.

19. The RFID tag of claim 1 , wherein said support has a generally trapezoidal cross-section.

20. The RFID tag of claim 1 , wherein said support has a generally arcuate cross-section.

21. The RFID tag of claim 1 , wherein said support has a generally triangular cross-section.

22. The RFID tag of claim 1 , wherein said support has a generally polygonal cross-section.

23. The RFID tag of claim 1 , wherein said support has a generally curvilinear cross-section.

24. The RFID tag of claim 1 , wherein said support comprises a housing which encloses said RF transponder.

25. An RFID tag, comprising: means for communicating information with an RFID system; means for forming a conducting ground plane; and means for holding said communicating means at a distance from the conducting ground plane.

26. A RFID system, comprising: an interrogator including an RF transmitter, an RF receiver, and an antenna for communicating information via transmitted and received RF signals; and an RFID tag including: an RF transponder configured to communicate information with said interrogator, the RF transponder including a dipole; a base plate forming a conducting ground plane; and a support attached to the base plate for retaining the RF transponder so that the dipole is held at a distance from the conducting ground plane.

27. The RFID system of claim 26, wherein the RF transponder further comprises: a substrate mounted to the support and carrying the dipole; and an RFID IC mounted to the substrate and coupled to the dipole.

28. The RFID system of claim 27, wherein the RFID IC is packaged within a package mounted to the substrate and wherein the package interconnects the RFID IC to the dipole.

29. The RFID system of claim 28, wherein the package is a small outline (SO) package.

30. The RFID system of claim 26, wherein the antenna has a simple dipole structure.

31. The RFID system of claim 26, wherein the antenna has a folded dipole structure.

32. The RFID system of claim 26, wherein the antenna has a meander dipole structure.

33. The RFID system of claim 26, wherein the impedance of the antenna is adjusted by modifying at least one of the width of the dipole, the length of the dipole, the distance between the dipole and the conducting ground plane, the size of the conducting ground plane.

34. The RFID system of claim 26, wherein the antenna includes a tuning stub comprising parallel stub lines.

35. The RFID system of claim 34, wherein the impedance of the antenna may be adjusted by modifying at least one of the width of the tuning stub, the length of the tuning stub, the distance of the tuning stub from the center of the dipole, and the edge to edge space between the stub lines.

36. The RFID system of claim 26, wherein the base plate is made of metal.

37. The RFID system of claim 36, wherein the metal is selected from the group consisting of aluminum, steel, brass, titanium, and copper.

38. The RFID tag of claim 26, wherein said base plate is made of a metallized material.

39. The RFID tag of claim 38, wherein the metallized material is a metallized plastic.

40. The RFID tag of claim 38, wherein the metallized material is a metallized mesh.

41. The RFID tag of claim 26, wherein a dimension of said base plate is approximately one half wavelength.

42. The RFID tag of claim 26, wherein said support holds said RF transponder above the conducting ground plane at a distance of approximately 7 percent to 11 percent of a wavelength.

43. The RFID tag of claim 26, wherein said support has a generally rectangular cross-section.

44. The RFID tag of claim 26, wherein said support has a generally trapezoidal cross-section.

45. The RFID tag of claim 26, wherein said support has a generally arcuate cross-section.

46. The RFID tag of claim 26, wherein said support has a generally triangular cross-section.

47. The RFID tag of claim 26, wherein said support has a generally polygonal cross-section.

48. The RFID tag of claim 26, wherein said support has a generally curvilinear cross-section.

49. The RFID tag of claim 26, wherein said support comprises a housing which encloses said RF transponder.