Abstract:
Described are antenna assemblies and methods for forming antenna assemblies. An antenna assembly includes a dual polarized far-field antenna and a near-field loop antenna. The near-field loop antenna is electromagnetically coupled to the dual polarized far-field antenna. The near-field loop antenna includes two contacts for electrically connecting to a chip.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to RFID antenna assemblies and methods for forming RFID antenna assemblies. 
     BACKGROUND OF THE INVENTION 
     Radio-Frequency Identification (RFID) technology is directed to wireless communication between one object, typically referred to as a RFID tag, and another object, typically referred to as a RFID reader/writer. RFID technology has been adopted, and is increasingly being used, in virtually every industry, including, for example, manufacturing, transportation, retail, and waste management. As such, efficient RFID systems are becoming increasingly important as the demand for RFID technology increases. 
     RFID tags typically include two components: a RFID antenna assembly and an RFID integrated circuit (IC). RFID antennas can be used to receive and/or transmit an electromagnetic signal from a RFID reader/writer. A RFID IC (sometimes referred to as a RFID chip) can be used to store and/or process information (e.g., modulate/demodulate a radio-frequency (RF) signal). 
     Typically, RFID systems that operate in the ultra-high frequency (UHF) range utilize a standard dipole antenna configuration for the RFID antenna assembly. The performance of a standard dipole UHF transponder depends on the orientation between the transponder antenna and the reader antenna, because dipole antennas can only emit radio signals in one direction. To achieve two-dimensional readability, two or more dipole antennas can be used in a single antenna assembly. For example, two dipole antennas can be arranged perpendicular to each other to form a “double-dipole” antenna, which takes the shape of a cross. Standard “double-dipole” antennas require RFID chips with at least three electrical contact points: two antenna inputs and one ground contact. In other words, RFID chips require a separate channel for each dipole of the antenna assembly. 
     SUMMARY OF THE INVENTION 
     One approach to providing two-dimensional readability is to couple a near-field loop antenna with a dual polarized far-field antenna. In one aspect, there is an antenna assembly for two-dimensional readability. The antenna assembly includes a dual polarized far-field antenna and a near-field loop antenna electromagnetically coupled to the dual polarized far-field antenna. The near-field loop antenna includes two contacts for electrically connecting to a chip. 
     In another aspect, there is a method for forming an antenna assembly. The method includes forming, on a first side of a first substrate, a dual polarized far-field antenna, and forming, on a second side of a second substrate, a near-field loop antenna on a-second layer. The near-field loop antenna includes two contacts for electrically connecting to a chip. The dual polarized far-field antenna is electromagnetically coupled to the near-field loop antenna. 
     In other examples, any of the aspects above can include one or more of the following features. The chip can include an RFID device. The dual polarized far-field antenna can be a UHF antenna. The near-field loop antenna can be inductively coupled to the dual polarized far-field antenna. The near-field loop antenna can be ohmically coupled to the dual polarized far-field antenna. The near-field loop antenna can be capacitively coupled to the dual polarized far-field antenna. The near-field loop antenna can be coupled to the dual polarized far-field antenna inductively, ohmically, capacitively, or any combination thereof. 
     In some embodiments, the dual polarized far-field antenna can include a far-field loop antenna. The far-field loop antenna can include a rectangular geometry, a fractal geometry or a symmetrical geometry. The antenna assembly can further include the chip. The chip can be a one-channel chip. The chip can be a multi-channel chip comprising three or more contact pads. The antenna assembly can further include a first layer, a second layer, and a third layer. The first layer can include metallization of the dual polarized far-field antenna. The second layer can include a carrier material. The third layer can include metallization of the near-field loop antenna. 
     In other examples, the antenna assembly can further include a first layer and a second layer. The first layer can include a carrier material. The second layer can include metallization of the dual polarized far-field antenna and metallization of the near-field loop antenna. The antenna assembly can further include a first carrier material including the dual polarized far-field antenna, and a second carrier material including the near-field loop antenna. 
     In yet other embodiments, the method can further include ohmically coupling the dual polarized far-field antenna to the near-field loop antenna. The method can further include forming segments of the dual polarized far-field antenna and the near-field loop antenna, wherein the segments inductively couple the dual polarized far-field antenna to the near-field loop antenna. The method can further include forming segments of the dual polarized far-field antenna and the near-field loop antenna, wherein the segments capacitively couple the dual polarized far-field antenna to the near-field loop antenna. 
     In yet other examples, the first and second substrates can be different and the method can further include positioning the first and second substrates together using lamination, dispensing, bonding, or any combination thereof. The first and second substrates can be the same and the first and second sides can be the same. The first and second substrates can be the same and the first and second sides can be different. The method can further include attaching the second substrate to a device, wherein forming the dual polarized far-field antenna can include printing the dual polarized far-field antenna over the second substrate attached to the device. 
     Any of the above implementations can realize one or more of the following advantages. By coupling a near-field loop antenna to a dual polarized far-field antenna, two-dimensional readable RFID tags can be made compatible with single-channel RFID chips. In addition, the RFID tags can remain compatible with multi-channel RFID chips. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Further features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the invention described above, together with further advantages, will be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
         FIGS. 1A-1B  are top views of a chip and a near-field loop antenna. 
         FIGS. 2A-2F  are top views of different antenna assembly configurations. 
         FIGS. 3A-3C  are cross-sectional side views of different antenna assembly substrate configurations of  FIG. 2A . 
         FIGS. 4A-4B  is a side view of a dual far-field antenna configuration. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1A  is a top view of an exemplary chip  110 . The chip  110  includes at least two contacts  112  and  114 . The contact  112  can be, for example, an antenna port. The contact  114  can be, for example, a ground port. Combined, the contacts  112  and  114  can form a single channel for communicating with a remote reader (not shown) via an antenna assembly. In one embodiment, for example, the chip  110  can include a RFID IC (sometimes referred to as a RFID chip). In a supplemental or alternative embodiment, the chip  110  can process UHF (ultra-high frequency) signals. 
     The chip  110  illustrated in  FIG. 1A  includes two contacts positioned in separate corners, but other configurations can also be used. For example, the chip  110  can include additional contacts. In one embodiment, a chip  110  with additional contacts can be used as a multi-channel chip for use with an antenna assembly with two or more channels. For example, a chip with two pairs of contacts that are associated with two chip channels can be connected to an antenna assembly with two separate antenna channels, in which each chip channel transmits and/or receives electromagnetic signals via their respective antenna channel. In yet other configurations, the contacts  112  and  114  can be located at arbitrary positions on the chip  110 . 
       FIG. 1B  is a top view of an exemplary near-field loop antenna  120 . The near-field loop antenna  120  includes a gap  125  between the contact points  122  and  124 . The contact points  122  and  124  can be used to connect to a channel on a chip. For example, the chip  110  can be coupled to the near-field loop antenna  120  by respectively attaching the contact points  122  and  124  to the chip contacts  112  and  114 . In one embodiment, the near-field loop antenna  120  can be attached to the chip  110  using flip chip bonding. In another embodiment, the near-field loop antenna  120  can be attached to the chip  110  using wire bonding. In yet another embodiment, the near-field loop antenna  120  can be fabricated on the same substrate as the chip  110 . 
     The near-field loop antenna  120  illustrated in  FIG. 1B  is configured as a circular loop, but other configurations can also be used. In one embodiment, for example, the near-field loop antenna  120  can be configured as a square loop or as any rotationally symmetric loop. More generally, the near-field loop antenna  120  can be configured in any arbitrary loop path. In some embodiments, the length of the near-field loop antenna  120  can be between 15 mm and 120 mm. The length of the near-field loop antenna  120  can depend on the electrical characteristics of the RFID chip (e.g., impedance, inductivity and/or capacitance). 
       FIGS. 2A-2F  are top views of different antenna assembly configurations  200 . The antenna assembly  200   a  includes a dual polarized far-field antenna  210  and a near-field loop antenna  120 . A chip  110  can be connected to the near-field loop antenna  120 . The dual polarized far-field antenna  210  advantageously can receive and/or transmit electromagnetic waves independent of the polarization of the electric field incident on the plane of the antenna  210 . In some embodiments, the length of the dual polarized far-field antenna  210  can be between 240 mm and 400 mm. The length of the far-field antenna  210  can depend on the electrical characteristics of the RFID chip, the quality factor of the coupling to the far-field antenna, and/or the application (e.g., based on the mounting of an RFID tag to any surface resulting in any detuning). Therefore, the resonance frequency of a RFID tag, and consequently the length of the far-field loop  210 , can be dependent on the application. 
     The near-field loop antenna  120  can be positioned into a corner  212  of the dual polarized far-field antenna  210  such that the two antennas are magnetically coupled to each other. For example, the near-field loop antenna  120  can be magnetically coupled to the dual polarized far-field antenna  210  via the magnetic induction that results from the proximity of segments of the two antennas in corner  212 . In some configurations, the near-field loop antenna  120  can overlap with the dual polarized far-field antenna  210  or a gap can exist between the two. In a supplemental or alternative embodiment to inductive coupling, the near-field loop antenna  120  can be ohmically and/or capacitively coupled to the dual polarized far-field antenna  210 . For example, the antenna assemblies  200   b  and  200   c  include a dual polarized far-field antenna  220  that is ohmically connected to the near-field loop antenna  120  via connections in corners  222   b  and  222   c . Generally, the far-field antenna  210  can connect to at least one point anywhere on the near-field antenna  120  (e.g., the point that is substantially opposite to the chip&#39;s position). 
     In the antenna assembly configurations  200   a - c , the dual polarized far-field antennas  210  and  220  are configured as rectangular loops, but other configurations can also be used. In one embodiment, for example, a dual polarized far-field antenna can be configured as any rotationally symmetric loop. More generally, a dual polarized far-field antenna can be configured in any arbitrary loop path. In some embodiments, for example, an antenna assembly configuration  200   d  or  200   e  can include a rectangularly-shaped dual polarized far-field antennas  230   d  or  230   e  with semi-circle indentations  232  located on each side. In an alternative embodiment, an antenna assembly configuration  200   f  can include a dual polarized far-field antenna  240  with a fractal geometry. The near-field loop antenna  120  can be positioned, for example, in the center of the dual polarized far-field antenna  240 , which would allow substantially all segments of the near-field loop antenna  120  to be magnetically coupled to segments  242  of the dual polarized far-field antenna  240 . 
     In general, near-field loop antennas and dual polarized far-field antennas can be formed on one or more substrates. Formation of an antenna can include metallization of a side of the substrate. Suitable substrates can include a non-conductive carrier material such as, for example, PET (polyester), FR-4 (or any other printed circuit board (PCB) material), PI (polyimide), BT (bismaleimide-triazine), PE (polyethylene), PVC (polyvinylchloride), PC (polycarbonate), Teslin (silica-filled polyethylene), paper and/or other suitable antenna substrate materials. In addition, substrates can be flexible or rigid. In one embodiment, a near-field loop antenna and a dual polarized far-field antenna can be formed on the same side of a substrate. In an alternative embodiment, a near-field loop antenna and a dual polarized far-field antenna can be formed on different sides of a substrate. In yet another embodiment, a near-field loop antenna and a dual polarized far-field antenna can be formed on different substrates and subsequently brought together using lamination, dispensing, bonding, and/or any other substrate binding process. 
     In another embodiment, a RFID chip can be bonded to a near-field loop (e.g., an antenna on a carrier material like PET), and the far-field antenna can be printed on the top-side or bottom-side of the carrier material. In yet another embodiment, a RFID chip can be bonded to a near-field loop (e.g., an antenna on a carrier material like PET), and the near-field loop can be laminated, dispensed, bonded, or otherwise attached to any device (e.g., a cardboard box or other housing). A far-field loop antenna can be printed on top of the device to which the near-field loop is attached to. 
       FIGS. 3A-3C  are cross-sectional side views of exemplary antenna assembly substrate configurations  300  using, for example, the antenna assembly  200   a  along the cross-section  301 . In antenna assembly substrate configuration  300   a , the near-field loop antenna  120  and the dual polarized far-field antenna  210  were formed on different sides of a substrate  310 , and can be inductively, capacitively, and/or ohmically coupled to one another. In antenna assembly substrate configuration  300   b , the near-field loop antenna  120  and the dual polarized far-field antenna  210  were formed on the same side of a substrate  320 , and can be inductively, capacitively and/or ohmically coupled to one another. In antenna assembly substrate configuration  300   c , the near-field loop antenna  120  and the dual polarized far-field antenna  210  were formed, respectively, on substrates  330   a  and  330   b . Substrates  330   a  and  330   b  can, for example, be brought together such that the near-field loop antenna  120  and the dual polarized far-field antenna  210  are inductively, capacitively, and/or ohmically coupled to one another. In one embodiment, a material, such as an insulator, can separate substrates  330   a  and  330   b . The substrates  300   a  and  300   b  can be brought together in any configuration (i.e., the surfaces on which the antennas were formed can both point away from each other, can both point towards each other, or can both point in the same direction). 
     In some embodiments, a dual polarized far-field antenna can be coupled to one or more additional dual polarized far-field antennas via inductive, capacitive, and/or ohmic coupling.  FIGS. 4A-B  are views of a dual far-field antenna assembly  400   a . The dual far-field antenna assembly  400   a  includes the dual polarized far-field antenna  210  and near-field loop antenna  120  as illustrated in  FIG. 2A  with an additional dual polarized far-field antenna  410 . The dual polarized far-field antenna  410  can be inductively coupled to the dual polarized far-field antenna  210 . The dual far-field antenna assembly  400   a  can be positioned on a device  420  (e.g., a cardboard box or other container) such that each far-field antenna is aligned with a different surface or direction. Providing different directional alignments of multiple far-field antennas advantageously can allow for better readability between a RFID tag and a RFID reader/writer. 
     One skilled in the art will realize the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.