Patent Publication Number: US-7898482-B2

Title: Conducting radio frequency signals using multiple layers

Description:
TECHNICAL FIELD 
     This invention relates to detecting radio frequency signals and, more particularly, to conducting radio frequency signals using multiple layers. 
     BACKGROUND 
     In some cases, an RFID reader operates in a dense reader environment, i.e., an area with many readers sharing fewer channels than the number of readers. Each RFID reader works to scan its interrogation zone for transponders, reading them when they are found. Because the transponder uses radar cross section (RCS) modulation to backscatter information to the readers, the RFID communications link can be very asymmetric. The readers typically transmit around 1 watt, while only about 0.1 milliwatt or less gets reflected back from the transponder. After propagation losses from the transponder to the reader the receive signal power at the reader can be 1 nanowatt for fully passive transponders, and as low as 1 picowatt for battery assisted transponders. At the same time other nearby readers also transmit 1 watt, sometimes on the same channel or nearby channels. Although the transponder backscatter signal is, in some cases, separated from the readers&#39; transmission on a sub-carrier, the problem of filtering out unwanted adjacent reader transmissions is very difficult. 
     SUMMARY 
     The present disclosure includes a system and method for conducting radio frequency signals using multiple layers. In some implementations, a signal transfer element configured to passively transfer RF signals between a first region and a second region includes a first conductor layer having a first continuous conductor configured as a first portion of a first antenna, a transmission line, and a first portion of a second antenna. The first antenna and the second antenna are configured to wirelessly receive and transmit Radio Frequency (RF) signals. The signal transfer element also includes a second conductor layer having a second continuous conductor configured as a second portion of the first antenna, a ground plane, and a second portion of the second antenna. The first conductor layer and the second conductor layer are spatially proximate such that the transmission line and the ground plane are configured to passively transfer RF signals between the first antenna and the second antenna independent of an electrical connection between the first conductor layer and the second conductor layer. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a transfer system for passively transferring radio frequency signals; 
         FIGS. 2A-F  are block diagrams illustrating example energy transfer media; 
         FIG. 3  is a flow chart illustrating an example method for passively transferring radio-frequency signals; and 
         FIGS. 4A-C  are block diagrams illustrating example energy transfer media coupled to an RFID chip; and 
         FIG. 5  is a flow chart illustrating an example method for manufacturing energy transfer media. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  is a top-view block diagram illustrating an example system  100  for conducting radio frequency (RF) signals between antennas in accordance with some implementations of the present disclosure. For example, the system  100  may passively transfer RF signals between antennas independent of interconnects between conductor levels. In some implementations, the system  100  may include an energy transfer medium having multiple conductor levels. For example, the passive energy transfer medium may include a first level forming a leg for each of two antennas that is connected using grounding plane and a second level forming a different leg for each of the two antennas that is connected using transmission line. In these implementations, the system  100  may be configured such that the two conductor levels are spatially proximate such that RF signals are passively transferred between two antennas independent of an electrical connection between the two conductor levels (e.g., interconnects, vias). For example, the distance between the conductor levels may be 2 to 20 mils. In addition, each conductor level may be formed using a continuous conductor. A continuous conductor may be a conductor configured to transmit incident RF signals from one location to a different location independent of physical connections. For example, physical connections may include soldered connections, mechanical connections, and/or other electrical connections. In some implementations, each conductor level may be formed using striplines, microstrips, and/or other continuous conductors. In some implementations, the system  100  may include multiple ground planes spatially proximate a transmission line such that RF signals are transferred between antennas independent of interconnects, vias, discrete connectors, or other electrical connections. By passively transferring RF signals independent of electrical connections between conduction layers, the system  100  may decrease, minimize, or otherwise reduce the cost associated with passive transmission media by reducing the number of connections, the number of manufacturing steps, and/or attenuation of the RF signal being passively transferred. 
     In some implementations, the system  100  can passively transfer radio frequency signals to obstructed RF IDentifiers (RFIDs) using such energy transfer media. The system  100  may include goods at least partially in containers. In managing such goods, the system  100  may wirelessly transmit RF signals to request information identifying these goods. In some cases, the RF signals may be attenuated by, for example, other containers, packaging, and/or other elements. For example, the system  100  may include containers with RFID tags that are stacked on palettes and are not located on the periphery. In this case, RF signals may be attenuated by other containers and/or material (e.g., water). In some implementations, the system  100  may passively transfer RF signals to tags otherwise obstructed. For example, the system  100  may include one or more transfer media that passively transfers RF signals between interior tags and the periphery of a group of containers. 
     At a high level, the system  100  can, in some implementations, include a group  108  including containers  110   a - f , energy-transfer media  120   a - f , RFID tags  130   a - f , and readers  140   a - b . Each container  110  includes an associated RFID tag  130  that wirelessly communicates with the readers  140 . In some cases, the RFID tag  130  may reside in an interior region  116  of the group  108  not at or proximate the periphery  114 . In this case, the energy-transfer medium  120  may passively transfer RF signals between interior RFID tags  130  and the readers  140 . In other words, the transmission path between reader  140  and interior tags  130  may include both wired and wireless connections. For example, the group  108  may be a shipment of produce, and the containers  110  may be returnable plastic containers (RPCs) or crates, which are commonly used worldwide to transport produce. In some cases, produce is composed primarily of water, which may significantly attenuate RF signals and interfere with RFID tags  130   c - 130   f  in the interior region  116  from directly receiving RF signals. In this example, the energy transfer media  120  may transmit RF signals between the periphery  114  and the interior region  116  enabling communication between the RFID readers  140  and the RFID tags  130   a - f . The system  100  may allow the produce shipment to be tracked and/or inventoried more easily, since each RPC can be identified by RFID while the shipment is stacked or grouped. While the examples discussed in the present disclosure relate to implementing RFID in stacked or grouped containers, the system  100  may be useful in a variety of other implementations. In some examples, the system  100  may be applied to the top surface of pallets to allow communication with boxes stacked on the pallet. In some examples, the system  100  may be applied to cardboard boxes by placing the antennas on different surfaces and bending the transmission line around the edges and/or corners. 
     Turning to a more detailed description of the elements, the group  108  that may be any spatial arrangement, configuration and/or orientation of the containers  110 . For example, the group  108  may include stacked containers  110  arrange or otherwise positioned on a palette for transportation. In some implementations, the group  108  may be a horizontal two-dimensional (2D) matrix (as illustrated), a vertical 2D matrix, a 3D matrix that extends vertically and horizontally, and/or a variety of other arrangements. The group  108  may be arranged regardless of the orientation and/or location of the tags  130 . The containers  110  may be any article capable of holding, storing or otherwise at least partially enclosing one or more assets (e.g., produce, goods). For example, the containers  110  may be RPCs including produce immersed in water. In some implementations, each container  110  may include one or more tags  130  and/or energy-transfer media  120 . In some examples, the tag  130  and/or the media  120  may be integrated into the container  110 . In some examples, the tag  130  and/or the medium  120  can be affixed to the container  110 . In some implementations, one or more of the containers  110  may not include a tag  130 . In some implementations, the containers  110  may be of any shape or geometry that, in at least one spatial arrangement and/or orientation of the containers  110 , facilitates communication between one or more of the following: tags  130  of adjacent containers  110 , energy transfer media  120  of adjacent containers  110 , and/or between tags  130  and energy transfer media  120  of adjacent containers. For example, the geometry of the containers  110  may include right angles (as illustrated), obtuse and/or angles, rounded corners and/or rounded sides, and a variety of other features. In some implementations, the containers  110  may be formed from or otherwise include one or more of the following: cardboard, paper, plastic, fibers, wood, and/or other materials. In some implementations, the geometry and/or material of the containers  110  may vary among the containers  110  in the group  108 . 
     The energy transfer media  120  can include any software, hardware, and/or firmware configured to passively transfer RF signals between two antennas independent of electrical connections between conductor layers. For example, the media  120  may include a transmission plane and a ground plane for passively transferring RF signals between antennas without an electrical connection between the planes. In general, the media  120  may wirelessly receive an RF signal at one portion (e.g., first antenna) and re-emit the signal from a different portion of the media  120  (e.g., second antenna). The media  120  can, in some implementations, receive signals from or transmit signals to the RFID antennas  142 , the RFID tags  130 , and/or other energy-transfer media  120 . For example, the RFID reader  140  may transmit an RF signal incident the periphery  114 , and the media  120  may receive and re-transmit the signal to an interior tag  130 . In some implementations, the media  120  can be at least a portion of a communication path between the RFID reader  140  and the RFID tag  130 . For example, the media  120  may transfer RF signals between the periphery  114  and the interior  114  of the group  108 . In doing so, the media  120  may establish communication paths to tags  130  otherwise unable to directly communicate with the reader  140 . 
     In some implementations, the media  120  may include two continuous conductors such that each forms a different conductor layer and passively transfers RF signals independent of an electrical connection between the layers. As previously mentioned, such electrical connections may include vias, interconnects, and/or others. In some implementations, a first conductor level of the media  120  may form a first leg of each antenna such that each leg is connected by a ground plane, and a second conductor layer of the media  120  may form a second leg of each antenna such that each leg is connected by a transmission line. In the case that the conductor layers are spatially proximate, the media  120  may passively transfer RF signals independent of an electrical connection between the layers. For example, the media  120  may include a dielectric layer that separates the conductor layers by 20 mils or less. In some implementations, the media  120  may include one or more of the following: antennas, microstrips, striplines, and/or any other features that passively transfer RF signals. In some implementations, the media  120  may include multiple ground planes that are spatially proximate a transmission line. For example, the multiple ground planes may be formed by folding a ground plane around a transmission line. In addition, the media  120  may passively transfer RF signals between locations independent of physical connections along the transmission path. As mentioned previously, physical connections may include solder connections, mechanical connections, and/or other connections for connecting at least two elements of the media  120  (e.g., antenna legs and transmission line). In some implementations, each conductor layer of the energy transfer media  120  may be fabricated separately and later affixed to form the energy transfer media  120 . The media  120  may be fabricated separately from and later attached or otherwise affixed to the container  110 . The energy transfer media  120  may be integrated into at least a portion of the container  110 . For example, the container  110  may be an RPC with an energy transfer medium  120  built into its structure. The energy transfer media  120  may include a variety of geometries, placements and/or orientations with respect to the tags  130  and/or containers  110 . For example, the energy transfer media  120  may bend or curve around or through any interior or exterior feature of the container  110 , such as corners, edges and/or sides. In some implementations, the media  120  includes directional antennas configured to, for example, increase transmission efficiency. In some implementations, the media  120  may be, for example, approximately six inches, 14 inches, and/or other lengths. 
     The RFID tags  130  can include any software, hardware, and/or firmware configured to backscatter RF signals. The tags  130  may operate without the use of an internal power supply. Rather, the tags  130  may transmit a reply to a received signal using power stored from the previously received RF signals independent of an internal power source. This mode of operation is typically referred to as backscattering. The tags  130  can, in some implementations, receive signals from or transmit signals to the RFID antennas  142 , energy transfer media  120 , and/or other RFID tags  130 . In some implementations, the tags  130  can alternate between absorbing power from signals transmitted by the reader  140  and transmitting responses to the signals using at least a portion of the absorbed power. In passive tag operation, the tags  130  typically have a maximum allowable time to maintain at least a minimum DC voltage level. In some implementations, this time duration is determined by the amount of power available from an antenna of a tag  130  minus the power consumed by the tag  130  to charge the on-chip capacitance. The effective capacitance can, in some implementations, be configured to store sufficient power to support the internal DC voltage when the antenna power is disabled. The tag  130  may consume the stored power when information is either transmitted to the tag  130  or the tag  130  responds to the reader  140  (e.g., modulated signal on the antenna input). In transmitting responses, the tags  130  may include one or more of the following: an identification string, locally stored data, tag status, internal temperature, and/or others. 
     The RFID readers  140  can include any software, hardware, and/or firmware configured to transmit and receive RF signals. In general, the RFID reader  140  may transmit request for information within a certain geographic area, or interrogation zone, associated with the reader  140 . The reader  140  may transmit the query in response to a request, automatically, in response to a threshold being satisfied (e.g., expiration of time), as well as others events. The interrogation zone may be based on one or more parameters such as transmission power, associated protocol, nearby impediments (e.g., objects, walls, buildings), as well as others. In general, the RFID reader  140  may include a controller, a transceiver coupled to the controller (not illustrated), and at least one RF antenna  142  coupled to the transceiver. In the illustrated example, the RF antenna  142  transmits commands generated by the controller through the transceiver and receives responses from RFID tags  130  and/or energy transfer media  120  in the associated interrogation zone. In certain cases such as tag-talks-first (TTF) systems, the reader  140  may not transmit commands but only RF energy. In some implementations, the controller can determine statistical data based, at least in part, on tag responses. The readers  140  often includes a power supply or may obtain power from a coupled source for powering included elements and transmitting signals. In some implementations, the reader  140  operates in one or more of frequency bands allotted for RF communication. For example, the Federal Communication Commission (FCC) have assigned 902-928 MHz and 2400-2483.5 MHz as frequency bands for certain RFID applications. In some implementations, the reader  140  may dynamically switch between different frequency bands. 
     In one aspect of operation, the reader  140  periodically transmits signals in the interrogation zone. In the event that the transmitted signal reaches an energy transfer medium  120 , the energy transfer medium  120  passively transfer the incident RF signal along a continuous conductor to different location and re-transmit the RF signal. The re-transmitted signal may then be received by another energy transfer medium  120 , a tag  130 , or a reader  140 . 
       FIGS. 2A-F  are diagrams illustrating example energy transfer media  120  for passively transferring RF signals using multi-conductor layers independent of electrical connections.  FIG. 2A  is a plan view of energy transfer medium  120 , which includes antennas  202   a ,  202   b  and a passive transmission path  204 .  FIGS. 2B and 2C  illustrate the energy transfer medium cross sections  206  and  208 , respectively.  FIG. 2D  is a plan view of energy transfer medium  120 , which includes antennas  202   a ,  202   b  and passive transmission path  204 .  FIGS. 2E and 2F  illustrate the energy transfer medium cross sections  210  and  212 , respectively. 
     Each of the antennas  202   a  and  202   b  includes two antenna legs  214 . The antenna  202   a  includes legs  214   a  and  214   b . The antenna  202   b  includes the antenna legs  214   c  and  214   d . The passive transmission path  204  include a transmission line  216  and a ground plane  218 . In some implementations, the transmission line  216  and the ground plane  218  are microstrips. The passive transmission path  204  of  FIG. 2D  includes a transmission line  216  and ground planes  218   a - c . In some implementations, the transmission line  216  and the ground planes  218   a - c  can be a printed pattern of conducting material such as a copper pattern printed on Mylar. As illustrated, the conductor layer  220  including the leg  214   b , the ground plane  218 , and the leg  214   d  are printed as a first continuous conductor, and the second conductor layer  222  including the leg  214   a  , the transmission line  216 , and the leg  214   c  are printed as a second continuous conductor. 
     Turning to  FIG. 2A , the passive transmission path  204  may passively transfer signals between the antennas  202   a  and  202   b . For example, the first antenna  202   a  may receive an RF signal (e.g., wirelessly from a reader  140 ), the passive transmission path  204  may transfer the signal to the second antenna  202   b , and the second antenna  202   b  may retransmit the signal (e.g., for wireless communication with a tag  130 ). In the illustrated examples, the energy transfer media  120  each include multiple substantially planar layers of conducting material and/or insulating material. However, in some implementations, the energy transfer media  120  are implemented as three dimensional structures. For example, the energy transfer medium  120  may bend, curve or otherwise deviate to accommodate the shape or contents of a container  110 . 
     The energy transfer medium  120  illustrated in  FIG. 2A  is implemented as a layered structure. The layered structure forming the energy transfer medium  120  may be implemented independent of wirings, solder, and/or other electrical connections (e.g., vias) between the conductor layers. Two cross-sectional views illustrating the layers of the energy transfer medium  120  at axes  206  and  208  are illustrated in  FIGS. 2B  and  2 C respectively. The layered structure may include alternating layers of conducting material and insulating material. The first conductor layer  220  (illustrated gray) includes the leg  214   b , the ground plane  218  and the leg  214   d . A first insulating layer  226  separates the first conductor layer  220  and a second conductor layer  222  (illustrated black). The second conductor layer  222  includes the leg  214   a , the transmission line  216  and the leg  214   c . A second insulating layer  228  is illustrated adjacent to the second conductor layer  222 , opposite the first insulating layer  226 . The layered structure may be fabricated, for example, by printing conducting strips on a substrate of insulating material. For example, the conductor layer  220  may be printed on the insulating layer  226 , the conductor layer  222  may be printed on the insulating layer  228 , and the two resulting structures may be attached using, for example, an adhesive. Alternatively, the layered structure may be fabricated by printing the conducting material on either side of a single insulating material substrate. For example, the conductor layer  220  may be printed on a first side of an insulating layer, and the conductor layer  222  may be printed on the other side of the same insulating layer. The insulating layers  226  and  228  may be made of any appropriate insulating material, such as Mylar. The thickness of the insulating layer may be determined by the specifications of the energy transfer medium  120 , by the fabrication process or materials, and/or by the specifications of the container  110 . In some example implementations, the insulation layers  226  and  228  can range from 2 to 10 millimeters thick, but the insulation layers  410  may be a different thickness according to other implementations. 
       FIG. 2B  is a cross-sectional view of the example passive transmission path  204 , along the axis  206 . The insulating layer  226  separates the ground plane  218  from the transmission line  216 . These three layers  216 ,  218 , and  226 , which may extend from the first antenna  202   a  to the second antenna  202   b , may define a microstrip for transferring RF signals between the two antennas  202   a  and  202   b . The ground plane  218  may serve as a ground or reference plate for the microstrip transfer line. In the illustrated example, the ground plane  218  is wider than the transmission line  216 . However, the transmission line  216  and the ground plane  218  may be in a different relative proportion in other implementations. For example, the ground plane  218  may, in some implementations, be wider than or the same width as the transmission line  216 . The transmission line  216  and the ground plane  218  may define a primary axis  230  of the passive transmission path  204 . The illustrated axis  230  extends straight in the direction substantially perpendicular to the antennas  202   a  and  202   b . However, in some implementations, the primary axis  230 , as defined by the transmission line  216  and the ground plane  218 , can bend, curves or otherwise deviate along a contour, edge, and/or corner of a container  110 . 
       FIG. 2C  is a cross-sectional view of the example antenna  202   b , along the axis  208 . The insulating layer  226  separates the leg  214   d  from the leg  214   c . The two legs  214   c  and  214   d  define a primary axis  232  of the antenna  202   b . The illustrated axis  232  extends straight in the direction substantially perpendicular to the passive transmission path  204 . However, in some implementations, the primary axis  232 , as defined by the legs  402   c  and  402   d , bends, curves or otherwise deviates along, for example, a contour, edge, and/or corner of a container  110 . The antennas  202   a  and  202   b  may be implemented as biplanar structures with no interconnections between the two layers. Additionally, the antennas  202   a  and  202   b  may be connected to the passive transmission path  204  without conductive interconnections between the two layers. The separation distance between the two planes, as defined by the insulating layer  226 , may be small enough that the antenna functions substantially as a single plane antenna. For example, compared to the length scales of the RF signals transmitted and received by the antennas  202   a  and  202   b , the thickness of the insulating layer  226  may be very small such as 100 times smaller. As a specific example, a 900 MHz RF signal received by the antenna  202   a  has a wavelength of approximately 300 millimeters, and the thickness of the insulating layer  226  may be 10 millimeters. 
     In one aspect of operation, the antenna  202   a  wirelessly receives an RF signal transmitted from a reader  140 . The received RF signal is transferred along the transmission path  204  to the antenna  202   b . Then the antenna  202   b  wirelessly re-transmits the received RF signal. The re-transmitted RF signal may then be received, for example, by another antenna  202  or a tag  130 . 
     In some implementations, the example energy transfer medium  120  illustrated in  FIGS. 2D-F  may include some of the same elements as the example energy transfer medium  120  illustrated in  FIGS. 2A-C . The energy transfer medium  120  of  FIGS. 2D-F  also includes two additional grounding planes  218   b  and  218   c  and an additional insulating layer  234 . As illustrated, the insulating layer  234  is adjacent to the conductor layer  228 . In some implementations, the insulating layer  234  can be omitted. The ground planes  218   b  and  218   c  may be included in the passive transmission path  204  to define a stripline transmission line configuration. For example, the conducting strip  218   b  may function as a second ground or reference plate, in addition to the ground plane  218   a . The insulating layers  228  and  234  separate the transmission line  222  from a third ground plane  218   c . The ground plane  218   c  is connected to the ground plane  218   a  by the ground plane  218   b . The stripline configuration of  FIGS. 2D-F  may be formed from the microstrip configuration of  FIG. 2A-C  by folding a portion of the ground plane  218  up and around the transmission line  216  (e.g., folding a portion of  218  out of the page, in  FIG. 2A ). In this way, the passive transmission path  204  of  FIGS. 2D-F  may be implemented without vias, soldered connections, and/or other connections between the conductor layers. 
       FIG. 3  is a flow chart illustrating an example method  300  for passively transferring RF signals between a first region of a container and a second region of the container. In particular, the example method  300  describes a technique for passively communicating RF signals using the energy transfer media  120  of  FIGS. 2A-C . The RF signal may be received from the readers  140 , the tags  130 , or a different energy transfer medium  120 . The method  300  is an example method for one aspect of operation of the system  100 ; a similar method, including some, all, additional, or different steps, consistent with the present disclosure, may be used to manage the system  100 . 
     The method  300  begins at step  302 , where an RF signal is wirelessly received using a first antenna. Next, at step  304 , the incident RF signal is passively transferred to a second antenna using a continuous conductor. For example, a leg of the first antenna, a transmission path, and a leg of the second antenna may be continuous conductor independent of physical connections (e.g., soldered connections). Finally, at step  306 , the RF signal is wirelessly re-transmitted using the second RF antenna. The re-transmitted RF signal may be received by a reader  140 , a tag  130 , or a different energy transfer medium  120 . 
       FIGS. 4A-C  illustrate an example energy transfer media  120  coupled to an RFID chip  402  in accordance with some implementations of the present disclosure. For example, the RFID chip  402  may be directly connected to the energy transfer media  120 . Referring to  FIG. 4A , the antenna  202   a  is coupled to the RFID chip  402  such that RF signals are passively transferred directly with the RFID chip  402 . In the illustrated implementation, the RFID chip  402  is at least coupled to the antenna  202   a  using the conductors  404   a  and  404   b . The conductors  404   a  and  404   b  may be positioned at least adjacent the RFID chip  402  and at least adjacent a portion of the legs  214   a  and  214   b , respectively. The conductors  404   a  and  404   b  may be a metal alloy including, for example, copper, silver, and/or other metals. In some implementations, the conductors  404   a  and  404   b  are electrically connected to the RFID chip using, for example, solder, pressed indium, and/or other types of connection. In some implementations, the antenna legs  214   a  and  214   b  are capacitively coupled to the conductors  404   a  and  404   b . The antenna legs  214   a  and  214   b  may passively transfer RF signals to the conductors  404 . 
     Referring to  FIG. 4B , the cross section  406  illustrates the RFID chip  402  directly connected to the antenna  202 . One end of the conductor  404  may be electrically connected to the RFID chip  402  and a different end may connected to the antenna leg  214 . The conductors  404  may be connected using any suitable electrical connections such as, for example, a soldered connection, a mechanical connection, and/or other types. In this implementations, RF signals are passively transferred between legs  214  and the RFID chip  402  using a direct electrical connection. In some implementations, a layer  408  may protectively cover the RFID chip  402  and conductors  404 . 
     Referring to  FIG. 4C , the cross section  406  illustrates the RFID chip  402  being capacitively coupled to the antenna  202 . In the illustrated implementation, the conductors  404  are spatially separated from the conductors  404  by a layer  408  such that the arrangement of the conductors  404 , the layer  408 , and the antenna legs  214  substantially form a capacitor. In doing so, RF signals may be passively transferred between the RFID chip  402  and the antenna  202   a  independent of an electrical connection. The layer  408  may be any suitable material such as a dielectric. In some implementations, the layer  408  is 20 mils or less. 
       FIG. 5  is a flow chart illustrating an example method  500  for manufacturing energy transfer media in accordance with some implementations of the present disclosure. In particular, the example method  500  describes a technique for manufacturing media  120  of  FIGS. 2A-F  using continuous conductors that are spatially proximate. The method  500  is an example method for one aspect of manufacturing; a similar method, including some, all, additional, or different steps, consistent with the present disclosure, may be used to manufacture media  120 . 
     The method  500  begins at step  502  where conductive patterns are generated on a thin substrates. For example, continuous conductors may be patterned on to a dielectric. In some implementations, the substrate may be 5 mils or less. At step  504 , the substrates including the patterns are cut into a one or more designs. In some implementations, the design may be rectangular or other polygonal shape. Next, at step  506 , an adhesive is applied to the substrates in at least locations that will overlap. In some implementations, an adhesive is applied to the location of the transmission line  216  and/or the ground plane  218 . The substrates are attached using the adhesive at step  508 . Returning to the example, the transmission line  216  and/or the ground plane  218  may be aligned and affixed to form the passive transmission path  204 . 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.