Abstract:
Where a single cable conveys bidirectional RF signals and bidirectional data using a data carrying DC power signal where the RF signals and the bidirectional data carrying DC power signal are separated using frequency selective networks. Alternatively a single cable conveys bidirectional RF signals and bidirectional data using a modulated RF data signal where the RF signals and the bidirectional modulated RF data signal are separated using frequency selective networks. A array of switchable antennas where RF switching elements are integral to the antennas is connected to the single cable and is powered by and communicated with through the cable. The array of switchable antennas can be arranged to produce an interrogation field in any of one, two or three dimensions by the antennas being arranged to provide for a series of parallel spaced conductors through which currents are sequentially switched in order to produce both tangential and normal magnetic field components. The spatial relationship of the sequentially switched currents is chosen to ensure that at different times a tangential and a normal magnetic field are produced at the same location. The conductors are preferably arranged in a planar fashion and the tangential and normal magnetic fields are produced above the planar surface. A single layer of parallel spaced conductors provides for one or two dimensional operations. Adding a second parallel layer of orthogonally oriented parallel spaced conductors provides three dimensional operations where currents are sequentially switched in both layers.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to the field of radio frequency identification (RFID). 
         [0002]    In one form, the invention relates to an interrogator antenna for interrogating an RFID transponder. 
         [0003]    The invention has been developed primarily for interrogating multiple passive transponders which are attached to objects to be identified by those respective transponders and will be described hereinafter with reference to that application. A typical application is the identification of RFID transponders or other RFID devices, such as those attached to documents or envelopes and embedded in plastic tokens or cards that are stacked on each other. 
         [0004]    It will be convenient to hereinafter describe the invention in relation to identification of RFID transponders; however it should be appreciated that the present invention is not limited to that use only. 
         [0005]    In one form, the invention provides a method by which data can be exchanged bi-directionally on a single cable between an interrogator and an RF signal control device. In another form, the invention provides a method of using a single cable port for controlling an RF signal and directing it to one of a number of output ports. In another form, the invention provides a way of controlling an RFID interrogation signal and directing it to one of many antenna coils. In another form, the invention provides a method by which data can be exchanged bi-directionally on a single cable between an interrogator and an antenna array in another form the invention relates to an interrogator including an arrangement of antenna coils with a single cable input port. In another form, the invention relates to a particular method of controlling antenna coils with a single cable input port. In another form, the invention relates to a method using a single cable input port for controlling antenna coils. 
         [0006]    The present invention has many applications, including any application where antennas are used to radiate fields, especially for the purpose of interrogation of a remote device. In a particular application, the present invention may be used in conjunction with RFID devices, such as, by way of example only, RF transponders, tags, tokens, labels, inlets, etc. Such devices may be used in a wide variety of applications, including, without limitation, article tracking such as shelving and storage systems, document management or article identification and/or sorting, gaming apparatus and gaming tokens, jewellery and diamond display and/or identification and/or tracking and luggage identification. 
         [0007]    It will be convenient to hereinafter describe the invention in relation to interrogating RFID devices, however it should be appreciated that the present invention is not limited to that use only. 
       BACKGROUND ART 
       [0008]    Throughout this specification the use of the word “inventor” in singular form may be taken as reference to one (singular) inventor or more than one (plural) inventor of the present invention. The discussion throughout this specification comes about due to the realisation of the inventor(s) and/or the identification of certain prior art problems by the inventors. 
         [0009]    Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein. 
         [0010]    It has been realised that in applications where RFID and remote powering is used and where orientation of the items to be identified cannot be guaranteed, such as shelving and storage systems, document tracking, luggage identification, gaming tokens, jewellery and diamond identification by way of example only, items to be identified may be missed and/or not correctly identified. 
         [0011]    The applicants are aware of a number of transponder systems that provide one dimensional, two dimensional, limited three dimensional or full three dimensional capability. These systems utilise a multiplicity of interrogator coils operating in different coordinate axis, to achieve two or three dimensional operation. 
         [0012]    One particularly advantageous interrogator design produces a uniform field in three dimensions. This form of interrogator is known as a Tunnel Reader Programmer (TRP). An example of a TRP for interrogating transponders on pallets or conveyors which meets all OH&amp;S and EM regulations in Australia is disclosed in U.S. Pat. No. 5,258,766 and international application PCT/AU95/00436. 
         [0013]    While a TRP has excellent three dimensional interrogation properties, a major drawback is that it is only suitable for applications where the RFID transponders are moved in and out of the TRP, usually on a conveyor or similar. TRP are inherently unsuitable for applications requiring the interrogation to occur on a flat surface such as a table or wall. For these applications flat planar antenna coils are required however these coils suffer from producing fields in only one direction at any point relative to the coil and do not have a two or three dimensional interrogation capability. 
         [0014]      FIG. 1  illustrates a conventional planar antenna coil arrangement, in which the coil  10  has windings  11  arranged in a somewhat circular configuration. 
         [0015]      FIG. 2  illustrates a cross sectional view X of  FIG. 1  of the windings of the coil of  FIG. 1 . The magnetic field created by inducing power into the windings is represented  12 . If a transponder  13  has a coil (not shown), but placed on it&#39;s outer top surface, for example, and if the transponder  13  is positioned substantially horizontally between the windings as illustrated in  FIG. 2 , the field  12  produced by the windings  11  has a correct orientation to power the transponder. Equally, if a transponder  14  is placed in a substantially vertical orientation as illustrated in  FIG. 2 , it too will be powered by the field  12 . However, if a transponder  15  is placed substantially horizontally near or outside the windings  11 , the field  12  generated by the windings will not be correctly oriented to power the transponder  15 . Likewise if the transponder is placed in a substantially vertical orientation in the inside of the windings  11  and  12  as illustrated in  16  the field  12  generated by the windings will not be correctly oriented to power the transponder  15 . 
         [0016]    A flat planar arrangement of antenna coils which can provide two dimensional or three dimensional interrogation is shown in international application WO 2007/030861A1. WO 2007/030861A1 is incorporated here in by reference. 
         [0017]    A one dimensional field can be generated over an extended area by overlapping planar coils that are switched in a sequential fashion. WO2007/030861A1 shows planar coils arranged in an overlapping fashion that are switched in a sequential fashion in order to generate a two dimensional interrogation field. WO 2007/030861A1 further shows that arranging a second layer of planar coils that are orthogonal to the first layer generates a three dimensional interrogation field. The coil antenna arrays for both the two dimensional and three dimensional operation are sequentially operated in order to provide their respective two and three dimensional interrogation fields. 
         [0018]      FIG. 3(   a ) illustrates the prior art coil arrangement  333  and  334  of WO 2007/030861 A1 where the coil windings  331  and  332  from several coils have been overlapped in order to form a series of parallel spaced conductors through which currents are sequentially switched in order to produce both tangential and normal magnetic field components. The spatial relationship of the sequentially switched currents is chosen to ensure that at different times a tangential and a normal magnetic field are produced at the same location. The conductors are preferably arranged in a planar fashion and the tangential and normal magnetic fields are produced above the planar surface. A single layer of parallel spaced conductors provides for two dimensional operations. 
         [0019]      FIG. 3(   b ) illustrates the prior art coil arrangement  333  of WO 2007/030861A1 where adding a second parallel layer  334  of orthogonally oriented parallel spaced conductors  332  provides three dimensional operations where currents are sequentially switched in both layers  331  and  332 . 
         [0020]    The amount of overlapping between the planar coils and the orthogonal coils can be adjusted to minimise the mutual coupling between the coils. This is advantageous as it reduces parasitic interactions between the coils. WO 89/10030 shows this method of minimising the mutual coupling between antenna coils which is advantageous for producing large arrays of many antennas. 
         [0021]    Producing a two or three dimensional interrogation field and minimising the mutual coupling may be contradictory requirements and other methods of reducing the effective coupling between coils may be required. The parasitic coupling between antenna can be reduced by using a switched device, or multiple switched devices, to open inactive antenna coils. Switch devices can be relays, MEMs or PIN diodes or any other device capable of interrupting an RF signal. PIN diodes are circuit elements specifically designed for the purpose of providing a controllable RF switch. The method of using PIN diodes to open circuit RF signals is described for example in WO2007/030861A1, WO2005/083893, WO2005/062421 and WO2000/067395. Opening the circuit of inactive antenna coils reduces the parasitic coupling between coils as little or no current can flow through the open switch(s) in the inactive coil(s). 
         [0022]    In order to sequentially operate the antenna arrays described in WO 2007/030861A1 the interrogating signal is sequentially switched to each antenna coil in the antenna array. An interrogator or reader with multiple outputs where the interrogation signal can be sequentially switched between the outputs is particularly advantageous for operating the antenna arrays described in WO 2007/030861A1. 
         [0023]    An example of such a reader is shown in U.S. Pat. No. 6,903,656 which shows a reader where an antenna switch is located at the output of the reader. The antenna switch is integral to the reader and is directly controlled by the reader&#39;s digital controller. Multiple antennas are operatively connected to the antenna switch by connecting cables. U.S. Pat. No. 6,903,656 is directed towards antenna tuning methods and does not deal with the application of the switched interrogation signal for generating two or three dimensional interrogation fields. 
         [0024]    There are applications where it is advantageous to move the antenna switch out of the reader and locate it remotely between the reader and the antennas connected to the switch. When positioned remotely the RF switch is called an RF multiplexer or RF MUX. The cable connections between the RF MUX and the antennas are considerably shorter. Remote positioning can save considerable cable length in installation since only a single cable connects the reader to the RF MUX replacing the multiple cables from the reader to each of the antenna that would have been required had the antenna switch been located in the reader. 
         [0025]    WO2007/094787A1 shows an RF MUX where the RF MUX is located remotely from the reader and is connected to the reader by a single antenna cable. The single antenna cable is used to convey the interrogation signal, DC power to power the MUX, modulations of the interrogation signal to control the MUX&#39;s operation and information from the MUX sent back to the reader by RF backscatter of the interrogation signal. The output ports of the MUX are connected to antennas or other MUXs by further cable. The method of using the RF interrogation signal for controlling the MUX and sending information as a backscatter signal back from the MUX to the reader requires complex RF circuits that can couple to, demodulate and backscatter the interrogation signal. A serious disadvantage of the method of data signalling described in WO2007/094787A1 is the circuit complexity and cost. 
         [0026]    Another problem exists whereby a person installing an RFID system and an antenna is coupled to a reader. However, the each antenna type has certain characteristics, and also each reader is usually configured to operate with a certain type of antenna. If an antenna is coupled to a reader, the reader should be configured to operate to that antenna type. However, this configuration is usually done manually, if it is done at all, and often, the configuration is not done correctly. 
         [0027]    Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein. 
       SUMMARY OF INVENTION 
       [0028]    An object of the embodiments described herein is to provide a simpler and cheaper method of controlling a remote RF MUX using a single connecting cable for both the RF signals and the control signals. 
         [0029]    Another object of the embodiments described herein is to provide a simpler and cheaper method of controlling an antenna array using a single connecting cable for both the RF signals and the control signals. 
         [0030]    Yet another object of the embodiments described herein is to provide a antenna design and/or interrogator which is more likely to enable powering and/or communication with an RFID device. 
         [0031]    A further object of the present invention is to alleviate at least one disadvantage associated with the prior art. 
         [0032]    It is still a further object of the embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of related art systems or to at least provide a useful alternative to related art systems. 
         [0033]    The present invention provides, according to one aspect of invention, a communication method and/or device adapted to enable communication between a first device and a second device, comprising providing a 1 st  signal representing a RF signal, providing a 2 nd  signal representing a power signal, providing a third signal representing a control and/or data signal, providing a communication path adapted to carry the 1 st ,2 nd  and 3 rd  signals, and wherein the 3rd signal is carried on the 1 st  and/or 2 nd  signal. 
         [0034]    In one embodiment, the 3rd signal is carried on the 1 st  signal. 
         [0035]    In another embodiment, the 3rd signal is carried on the 2 nd  signal. 
         [0036]    The present invention provides, according to another aspect of invention, a method of and/or device for coupling a first device to a 2 nd  device, comprising: 
         [0037]    providing a communication path between the 1 st  &amp; 2 nd  devices; 
         [0038]    providing an identification attribute in the 1 st  and/or 2 nd  device, communicating the attribute between to 1 st  &amp; 2 nd  devices and determining from the communication whether the 1 st  &amp; 2 nd  devices are correctly coupled. 
         [0039]    In one form, the invention relates to an identification system, and devices used in the system. Examples of the devices include transponders and/or apparatus adapted to be incorporated into items for storage on shelving and/or in storage systems. Another example of the devices includes transponders and/dr apparatus adapted to be incorporated into articles in a secure site, such as legal evidence samples which employ the use of a transponder and/or other identification device attached to the sample(s) for the purposes of monitoring and/or recording movements of the samples. Still another example of the devices includes tokens and/or apparatus adapted to be incorporated into gaming tables and/or devices. 
         [0040]    In another form, the invention relates to a system for monitoring and/or recording gaming transactions in a casino, such as gaming transactions which employ the use of a gaming token which token has a transponder and/or other identification device therein. 
         [0041]    In another form, the invention relates to a system for monitoring and/or recording jewellery or diamond movements or transactions, such as in an exchange, wholesaler or retailer where transactions which employ the use of a transponder and/or other identification device therein. 
         [0042]    Preferably, a method of reading is substantially in accordance with PCT/AU 2003/001072. 
         [0043]    Preferably, a method of reading is substantially in accordance with U.S. Pat. No. 5,302,954. 
         [0044]    Preferably, a method of power, interrogating and/or communicating with an RFID device is substantially in accordance with WO 9934526. 
         [0045]    Other aspects and preferred aspects are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention. 
         [0046]    In essence, an aspect of invention relates to communication between a first and second device, such as a switched antenna array connected to a reader by, preferably, a single cable. The single cable conveys RF signals and/or data (preferably bidirectionally, although communication in only one or both directions is also contemplated within the scope of the present invention) using a data carrying DC power signal where the RF signals and the data carrying DC power signal are separated. The manner of the separation may depend on the application. One preferred form of separation is using frequency selective networks. In one embodiment of the invention, an RE MUX is connected to the single cable and is powered by and communicated with through the cable. An array of antennas is connected to the RF MUX. The antennas and MUX circuits are integrated into a single switched antenna array where the RF switching elements are integral to the antennas. The array of switchable antennas can be arranged to produce an interrogation field in any of one, two or three dimensions by the antennas being arranged to provide for a series of parallel spaced conductors through which currents are sequentially switched in order to produce both tangential and normal magnetic field components. The spatial relationship of the sequentially switched currents is chosen to ensure that at different times a tangential and a normal magnetic field are produced at the same location. The conductors are preferably arranged in a planar fashion and the tangential and normal magnetic fields are produced above the planar surface. A single layer of parallel spaced conductors provides for one or two dimensional operations. Adding a second parallel layer of orthogonally oriented parallel spaced conductors provides three dimensional operations where currents are sequentially switched in both layers. 
         [0047]    Alternatively, a communication method may be used between a 1 st  &amp; 2 nd  device in which the 1 st  device transmits a control or data signal to the 2 nd  device using an RF signal which is modulated and/or switched. Corresponding receiving and/or demodulation circuitry is then provided in the 2 nd  device in order to receive the control or data signals. In one form, the RF signal is switched off for short periods of time, and the envelope of the RF signal is detected by a diode peak detection circuit. In another form the frequency of the control or data RF signal is not the same as the frequency of the RF signal. Frequency selective circuits separate the control or data RF signal from the RF signal. In essence, another aspect of invention is related to the coupling of a first and second device. In this aspect of invention, an attribute of any suitable form is used to verify and/or to determine the extent of the coupling of the devices. For example, the attribute may be a signal, coding, sequence, data and/or a form of identification. 
         [0048]    The present invention has been found to result in a number of advantages, such as:
       Provides for using a single cable for conveying RF signals and data using a data carrying DC power signal   Provides for using a single cable for conveying bidirectional RF signals and bidirectional data using a data carrying DC power signal   Provides for a simple method of operating a remote RF MUX using only a single cable for conveying bidirectional RF signals and bidirectional data using a data carrying DC power signal   Provides a simple planar antenna design which produces strong interrogation fields in one, two or three dimensions using a single cable for conveying bidirectional RF signals and bidirectional data using a data carrying DC power signal   Provides a simple planar antenna design which produces strong interrogation fields in one, two or three dimensions where only a single cable connects the planar antenna to a reader.   Provides a simple planar antenna design which produces strong interrogation fields with reduced radio emissions in one, two or three dimensions where only a single cable connects the planar antenna to a reader   Provides for a simple planar antenna ideally suited for table mounting or mounting to or as a flat surface onto which transponders may be place to be interrogated.   Depending upon the antenna design transponders can be interrogated regardless of their orientation in one, two or three dimensions.       
 
         [0057]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    Further disclosure, objects, advantages and aspects of the present application may be better understood by those skilled in the relevant art by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and in which: 
           [0059]      FIG. 1  illustrates a prior art antenna coil arrangement, 
           [0060]      FIG. 2  illustrates magnetic fields associated with the coil of  FIG. 1  as well as a number of transponder orientations, 
           [0061]      FIGS. 3(   a ) and  3 ( b ) illustrates the prior art antenna coil arrangement of WO 2007/030861A1 for producing two and three dimensional interrogation fields, 
           [0062]      FIG. 4  illustrates the prior art RF MUX circuit of WO 2007/094787A1, 
           [0063]      FIGS. 5(   a ) and  5 ( b ) illustrate embodiments for using a single cable for conveying RF signals and DC power, 
           [0064]      FIGS. 6(   a ),  6 ( b ) and  6 ( c ) illustrate how the embodiments shown in  FIGS. 5(   a ) and  5 ( b ) can use a single cable for conveying RF signals and bidirectional data using the DC power signal or an RF signal, 
           [0065]      FIG. 7  shows another embodiment of the use of a single cable for conveying RF signals and bidirectional data using a DC power signal, 
           [0066]      FIG. 8  shows yet another embodiment of the use of a single cable for conveying RF signals and bidirectional data using a DC power signal, 
           [0067]      FIGS. 9(   a ),  9 ( b ) and  9 ( c ) show yet other embodiments of the use of a single cable for conveying RF signals and data using a DC power signal, 
           [0068]      FIGS. 10(   a ) and  10 ( b ) show embodiments of an RF MUX circuit using a single cable for conveying RF signals and data using a DC power signal, 
           [0069]      FIG. 11  shows another embodiment of an RF MUX circuit using a single cable for conveying RF signals and data using a DC power signal, 
           [0070]      FIG. 12  shows yet another embodiment of an RF MUX circuit using a single cable for conveying RF signals and bidirectional data using a DC power signal, 
           [0071]      FIG. 13  shows yet another embodiment of an RF MUX circuit using a single cable for conveying RF signals and bidirectional data using a DC power signal, where antennas are an integral part of the MUX circuits. 
           [0072]      FIG. 14  shows an example circuit of an antenna incorporating an RF switch. 
           [0073]      FIG. 15  shows an example circuit for an antenna incorporating several RF switches. 
           [0074]      FIGS. 16(   a ) and  16 ( b ) show example circuits of antennas incorporating several RF switches. 
           [0075]      FIGS. 17(   a ) and  17 ( b ) show antenna arrays suitable for generating a sequentially switched interrogation field in at least one dimension. 
           [0076]      FIGS. 18(   a ) and  18 ( b ) show antenna arrays suitable for generating a sequentially switched interrogation field in at least two dimensions. 
           [0077]      FIGS. 19(   a ),  19 ( b )  19 ( c ) and  19 ( d ) illustrate how two panels of parallel sequentially switched conductors when placed parallel to each other with the conductors orthogonally orientated will produce a three dimensional field. 
           [0078]      FIGS. 20(   a ) and  20 ( b ) show arrays of antennas suitable for generating a sequentially switched interrogation field where the arrays are connected to a reader by a single cable. 
           [0079]      FIG. 21  shows an application for the invention where the invention is included in a shelving system. 
           [0080]      FIG. 22  shows another application for the invention where the invention is used to read closely stacked gem or jewellery transponders. 
           [0081]      FIG. 23  shows still a further application for the invention where the invention is used to read closely stacked gaming tokens. 
           [0082]      FIG. 24  shows still a further application for the invention where the invention is used to read closely stacked gaming tokens 
           [0083]      FIG. 25  shows still a further application for the invention where the invention is used to read closely stacked documents 
           [0084]      FIG. 26  shows still a further application for the invention where the invention is used to read displayed items 
           [0085]      FIG. 27  illustrates an alternative communication method and 
           [0086]      FIG. 28  illustrates another alternative communication method. 
       
    
    
     DETAILED DESCRIPTION 
       [0087]      FIG. 4  illustrates the prior art RF MUX circuit of WO2007/094787A1. The prior art RF MUX circuit of WO2007/094787A1 uses a single antenna cable  20 ′ to convey the interrogation signal, DC power  124  to power the MUX, modulations of the interrogation signal to control the MUX&#39;s operation and information from the MUX sent back to the reader by RF backscatter of the interrogation signal. The RF signals and DC power are separated using a frequency selective capacitor and inductor network  120  and C 1 . Bidirectional data is conveyed using the RF signal. The RF signal is modulated with data for the MUX where an RF coupler  130  and RF detector  132  extract and demodulate the data for the MUX. Data from the MUX is backscatter modulated  250  onto the RF signal and injected onto the cable  20 ′ through the RF coupler  130 . The RF coupler  130 , detector  132  and backscatter circuit  250  are complex and add unnecessary cost to the RF MUX. 
         [0088]      FIG. 5(   a ) illustrates an arrangement for using a single cable  51  for conveying RF signals  52  and DC power  53 . The RF signals and DC power are combined and separated using a frequency selective capacitor and inductor networks  54  and  55  at each end of the cable. The inductors  56  and  57  pass DC and low frequencies while the capacitors  58  and  59  stop DC and low frequencies and pass high frequency RF signals. More complex frequency selective circuits may be used if better frequency characteristics are desired. 
         [0089]      FIG. 5(   b ) shows more complex frequency selective circuits  54  and  55  where inductors  56  and  57  separate the DC signal  53 , band pass circuits  510  and  511  pass the RF signal  52  and high pass and/or band pass circuits  512  and  513  pass control or data RF signals  514 . 
         [0090]      FIG. 6(   a ) illustrates how the arrangement shown in  FIG. 5(   a ) can use a single cable for conveying bidirectional RF signals and bidirectional data using the DC power signal. The RF signals pass through the capacitors  68  and  69  at each end of the cable and are not able to pass through the inductors  62  and  64 . The DC voltage and current pass through the inductors  62  and  64  at each end of the cable and are not able to pass through the capacitors  68  and  69 . Power is conveyed from voltage source  61  to inductor  62  passes through the cable  63  and inductor  64  at the other end of the cable where it is used to provide electrical power  610 . Bidirectional data communication is achieved by using a voltage mode transmission in one direction and a current mode transmission in the reverse direction. The voltage applied by voltage source  61  passes through inductor  62 , cable  63  and inductor  64  at the other end of the cable where it is sensed by voltage sensor  65 . Data  611  is conveyed from voltage source  61  to voltage sensor  65  by amplitude modulation of the voltage source  61 . Current applied by current source  66  injects current through inductor  64 , cable  63  and inductor  62  to current sensor  67 . Data  612  is conveyed from current source  66  to current sensor  67  by amplitude modulation of the current source  66 . 
         [0091]    The equivalent dual circuit shown in  FIG. 6(   b ) can also be used for bidirectional communication. In the dual circuit voltage source  61  is replaced with a current source  613 , current source  66  is replaced with a voltage source  614 , voltage sensor  65  is replaced with a current sensor  615  and current sensor  67  is replaced with a voltage sensor  616 . Current source  613  injects current through inductor  62 , cable  63  and inductor  64  where it is used to provide electrical power  610 . Data  611  is conveyed from current source  613  to current sensor  615  by amplitude modulation of the current source  613 . Voltage applied by voltage source  614  to inductor  64  passes through inductor  64 , cable  63  and inductor  62  to voltage sensor  616 . Data  612  is conveyed from voltage source  614  to voltage sensor  616  by amplitude modulation of the voltage source  614 . The equivalent dual circuit shown in  FIG. 6(   b ) is electrically less efficient than the circuit shown in  FIG. 6(   a ). The circuit used in  FIG. 6(   a ) is used for the following description of the invention however the invention may equally be applicable to a dual. 
         [0092]      FIG. 6(   c ) illustrates how the arrangement of  FIG. 5(   b ) can use a single cable for conveying a DC power signal, bidirectional RF signals and bidirectional data using an RF signal. DC power  610  is conveyed from voltage source  623  to inductor  62  passing through the cable  63  and inductor  64  at the other end of the cable where it is used to provide electrical power  610 . The RF signal passes through the band pass filters  617  and  618  at each end of the cable. Bidirectional data passes through high pass filters  619  and  620  at each end of the cable. The bidirectional data RF signal is encoded and decoded by RF modems  621  and  622 . Depending upon the frequencies used by the bidirectional RF signal and bidirectional data RF signal different combinations of low pass, band pass or high pass filters may be advantageously used for elements  617 ,  618 ,  619  and  620  to separate the bidirectional RF signal and bidirectional data signal. RF modems  621  and  622  may advantageously use commercially available cheap short range RF modems, such as the IEEE 802.15.4 ‘ZigBee™’. 
         [0093]      FIG. 7  shows an example embodiment of the use of a single cable  73  for conveying bidirectional RF signals and bidirectional data  714  and  717  using a DC power signal  713 . The circuits required for bidirectional communication are very simple and extremely cheap. The voltage supply  713  is switched by data  714  using pass transistor  71 . When the transistor  71  is ON the supply voltage  713  passes through inductor  72 , cable  73 , inductor  74  and diode  75  to power storage capacitor  76 . The voltage  715  on power storage capacitor  76  is used to provide electrical power. When transistor  71  is turned OFF the voltage on inductor  72 , cable  73  and inductor  74  discharges to zero volts. A discharge resistor  712  can assist with speeding up the discharge if required. When transistor  71  is turned ON the voltage on the inductor  72 , cable  73  and inductor  74  is charged up to its full value. The change in voltage is sensed at the output of inductor  74  by transistor  77 . Resistor  716  serves as a base current limiter for transistor  77 . The transistor  78  and resistor  79  are a switchable current source controlled by data  717 . When the transistor  78  is ON a current equal to the supply voltage  713  divided by the resistor value  79  is drawn through inductor  74 , cable  73 , inductor  72  and current sense resistor  710 . The voltage across current sense resistor  710  is equal to the current multiplied by the sense resistor value. The change in current through the sense resistor is detected by transistor  711 . 
         [0094]      FIG. 8  shows yet another embodiment of the use of a single cable  83  for conveying bidirectional RF signals and bidirectional data  815  and  816  using a DC power signal  814 . The voltage supply  814  is switched by data  815  using pass transistor  81 . When the transistor  81  is ON the supply voltage passes through inductor  82 , cable  83 , inductor  84  and diode  85  to power storage capacitor  86 . The voltage on power storage capacitor  86  is regulated to a fixed DC voltage by regulator  812  and is used to provide electrical power. When transistor  81  is turned OFF the voltage on inductor  82 , cable  83  and inductor  84  discharges to zero volts. A discharge resistor  813  can assist with speeding up the discharge if required. When transistor  81  is turned ON the voltage on the inductor  82 , cable  83  and inductor  84  is charged up to it full value. The change in voltage is sensed at the output of inductor  84  by comparator  87 . The transistor  88  and resistor  89  are a switchable current source controlled by data  816 . When the transistor  88  is ON a current equal to the supply voltage  814  divided by the resistor value  89  is drawn through inductor  84 , cable  83 , inductor  82  and current sense resistor  810 . The voltage across current sense resistor  810  is equal to the current multiplied by the sense resistor value. The change in current through the sense resistor is sensed by comparator  811 . 
         [0095]      FIGS. 9(   a ),  9 ( b ) and  9 ( c ) shows yet other embodiments of the use of a single cable  90  for conveying bidirectional RF signals and bidirectional data using a DC power signal. 
         [0096]      FIG. 9(   a ) shows a two wire memory chip  91  connected to the circuit. A two wire memory chip uses two wires for reading and writing data. One wire  92  is for input data and the other wire  93  is for output data. Data is passed serially. The supply voltage  94  to the memory is maintained by the action of diode  95 , power storage capacitor  96  and voltage regulator  97 . The memory chip can be programmed with uniquely identifying data so that it can signal its identity and/or ‘type’ of device down the cable to the circuits/reader  910  at the other end of the cable. This is very useful where a new circuit  98  is connected to the cable  90  and allows the circuit  98  to identify itself, automatically or on demand, to the circuits  910  at the other end of the cable. The installation of new circuits  98  to the cable would then allow for automatic configuration and true ‘plug and play’ of these circuits without the need for manual configuration of the system. 
         [0097]      FIG. 9(   b ) shows a logic circuit  911  connected to the circuit. The logic circuit is a counter circuit which is clocked each time the DC power signal  912  is pulsed low. When transistor  913  is turned OFF the power supply voltage  912  supplied to the cable is disconnected and the voltage on the cable and at the counter circuit clock input  914  of the counter circuit discharges. A discharge resistor  918  can assist with speeding up the discharge if required. The supply voltage  915  to the counter circuit  911  is maintained by the action of diode  916  and power storage capacitor  917 . When transistor  913  is turned ON the clocking input is pulled high and the counter circuit will increment its count value. The counter circuit is configured to sequentially activate only one output line  918  at any time. The circuit shown in  FIG. 9(   b ) can be used to sequentially active other circuits connected to the counter circuit  911 . An example of a suitable counter circuit is the CD  4017  decade counter. The count length is set by connecting the chip reset to the appropriate decode output. 
         [0098]      FIG. 9(   c ) shows a micro-controller  919  connected to the circuit. Data  928  controls switching transistor  929  which controls the application of the DC supply voltage  930 . The transistor  920  is used to clock data  928  into the micro-controller. The supply voltage  921  to the micro-controller is maintained by the action of diode  922 , power storage capacitor  923  and voltage regulator  924 . The microcontroller can be used to control other circuits such as tuning control circuits, memory circuits, displays, lights and sounds for example. The micro-controller can also monitor circuit function and signal this functional information and any other reply data  931  back using the switched current source made from transistor  925  and resistor  926 . The reply data  913  is sensed by current sense resistor  932  and comparator  927 . The reply data  913  can include a pre-programmed identifier, pre-programmed data, circuit parameters such as voltage, current, phase, temperature or frequency and tuning parameters for example. 
         [0099]      FIG. 10(   a ) shows an RF MUX circuit using a single cable  103  for conveying RF signals and data using a DC power signal  103 . The RF MUX uses PIN diodes  101  to switch the RF signal passed through capacitor  102 , cable  103  and capacitor  104 . The DC supply voltage  103  passes through switch  105 , inductor  106 , cable  103 , inductor  107  and supplies electrical power  108  to control circuit  109 . Diode  1010  and power storage capacitor  1011  isolate the control circuit supply voltage  108  from pulses on the signalling voltage  1012  caused by switch  105 . The PIN diodes  101  are forward biased through current limiting resistor  1013  and inductor  1014 . The PIN diodes  101  are forward biased by closing their respective pull down switch  1015 . Inductor  1016  passes DC current and isolates the switch  1015  from the RF signal. Typically only one PIN diode is turned on at anytime. The remaining PIN diodes  101  are reverse biased through pull up resistor  1017 . Output capacitor  1018  passes the RF signal to the output port  1019  and isolates the DC voltage at the PIN diode cathode from the output port. The control circuit  109  controls the pull down switches  1015  and sequentially switches the diode switches. Signalling pulses from switch  105  transmit data to the control circuit and may direct its operation. A discharge resistor  1020  can assist with speeding up the discharge of the signalling voltage  1012  and a decoupling capacitor  1021  can reduce the RF voltage coupled through inductor  107 . 
         [0100]    In all of the circuit embodiments shown the supply voltage isolated by the diode and DC storage capacitor can be post regulated to a lower value by a voltage regulator circuit or boosted to a higher value by a voltage boost circuit. A lower voltage may be required by low voltage logic or microcontroller circuits for example and a higher voltage may be required by PIN diode switches for higher reverse biases. It is also possible that regulator or voltage boost circuits could be directly connected without the isolation diode and DC storage capacitor. 
         [0101]      FIG. 10(   b ) shows the RF MUX circuit of  FIG. 10(   a ) where, the supply voltage is post regulated to a lower value LV by a voltage regulator  1022  for logic or microcontroller circuits and boosted to a higher value HT by a voltage boost circuit  1023  to provide a higher reverse bias for the PIN diode switches. Current limiting resistor  1013  has been replaced by a current limiting circuit  1024  which could be a linear or switching current limiting circuit. 
         [0102]    While the embodiments show PIN diodes being used for RF switches other form of RF switches can be used such as relays or micro electro-mechanical switches (MEMS). 
         [0103]      FIG. 11  shows another embodiment of an RF MUX circuit using a single cable  110  for conveying bidirectional RF signals and data using a DC power signal  111 . A counter circuit  112  is clocked by pulses on the signalling voltage caused by transistor  113 . An example of a suitable counter circuit is the CD  4017  decade counter where the count length is set by connecting the chip reset to the appropriate decode output. The counter supply voltage  118  is isolated from the signalling pulses by diode  119  and DC storage capacitor  1120 . The counter outputs  114  are clocked sequentially. Only one output of the counter is active at any one time. The outputs of the counter  112  are connected to pull down transistors  114 . The voltage at the PIN diode  116  common node  115  approximately equals 1.0V being the PIN diode  116  forward voltage drop (0.8V) plus the pull down transistor  114  saturation voltage (0.2V). All PIN diodes are reverse biased by their respective pull up resistors  117 . The PIN diode reverse voltage is the DC supply voltage  111  less 1.0V. Decoupling capacitors  1121  and  1122  reduce the RF signal coupled through inductors  1123  and  1124 . PIN diode  116  forward bias current is limited by current limiting resistor  1125 . Inductor  1126  passes the DC bias current and isolates the circuit from the RF signal. The RF signals pass through the capacitors  1127  and  1128  at each end of the cable and are not able to pass through the inductors  1123 ,  1124  and  1126 . 
         [0104]      FIG. 12  shows yet another embodiment of an RF MUX circuit using a single cable  120  for conveying RF signals and bidirectional data using a DC power signal  121 . The DC power signal may be regulated to a lower voltage more suitable for a microcontroller by regulator  122 . The microcontroller  123  received data  127  from transistor  124 . The outputs of the microcontroller  125  are connected to pull down transistors  126 . The microcontroller controls its outputs under direction of data  127  sent as pulses of the power signal caused by switching transistor  128 . In one embodiment the microcontroller counts sequentially through its outputs. The voltage at the PIN diode  129  common node  1210  approximately equals 1.0V being the PIN diode  129  forward voltage drop (0.8V) plus the pull down transistor  126  saturation voltage (0.2V). All PIN diodes are reverse biased by their respective pull up resistors  1211 . The PIN diode reverse voltage is the DC supply voltage less 1.0V. If the reverse bias is not sufficiently large then a voltage boost circuit  1212  can be included to increase the PIN diode reverse bias voltage HT. The microcontroller is also able to send reply data  1213  by the switchable current source transistor  1214  and resistor  1215 . When the transistor  1214  is ON a current equal to the supply voltage  121  divided by the resistor value  1215  is drawn. The change in current is sensed at the other end of the cable by current sense resistor  1216  and comparator  1217 . The reply data  1213  can include an identification number, pre-programmed data or circuit parametric values such as voltage, current, phase, temperature or tuning state. For example a tuning detector circuit  1218  which provides a voltage proportional to the phase relationship between the RF signal voltage and current could be monitored by the microcontroller and the tuning state information returned as part of the reply data  1213 . Diode  1219  and DC storage capacitor  1220  isolate the LV and HT circuits from the power signalling pulses. Other sensors  1221  can also be monitored by the microcontroller and their state returned as part of the reply data  1213 . Temperature, current or voltage are examples of parameters that could be monitored. 
         [0105]      FIG. 13  shows an embodiment of an RF MUX which uses a single cable  130  for conveying RF signals and bidirectional data using a DC power signal  131  where switchable antennas  132  are an integral part of the MUX circuits. The MUX output ports have been replaced by switchable antennas  132 . Each antenna includes integral RF switches which are controllable by control ports  133 . The logic or control circuits  134 , data transmit and receive circuits  135 , power supply voltage regulator  136  for the LV supply, voltage boost circuit  137  for the reverse bias HT supply and the isolating diode  138  and DC storage capacitor  139  are contained in the circuit block  1310 . Individual control lines of the control bus  1311  from the logic or control circuits  134  control the switchable antennas  132  to be in an active or not active state. The antennas  132  can be individually switched by the logic or control circuits  134 . The reverse bias HT is supplied to the switchable antennas  132  for biasing integral PIN diode switches. Other RF switches such as relays or MEMs can be used instead of PIN diodes. The antennas  132  are switched in a sequential fashion by the control circuit  134  under direction of data  1312  sent from the circuits  1313  at the other end of the cable  130 . The data  1312  is received by the data receive circuits  135 . The control circuits  134  can transmit reply data  1314  to the circuits  1313  at the other end of the cable using the data transmit circuits  135 . Inductors  1315 ,  1316  and  1317  pass DC currents and isolate the circuit from the RF signal. RF switch forward bias current is limited by current limiting resistor  1318 . Decoupling capacitors  1319  and  1320  reduce the RE signal coupled through inductors  1315  and  1316 . The RF signals pass through the capacitors  1321  and  1322  at each end of the cable and are not able to pass through the inductors  1315 ,  1316  and  1317 . 
         [0106]      FIG. 14  shows an example circuit of an antenna incorporating an RF switch. A PIN diode RF switch  141  is forward biased by inductors  142 , current limit resistor  143 , pull down transistor  145  and inductor  144 . The diode is reverse biased by pull up resistor  146  when transistor  143  is OFF. The inductor  147  and capacitor  148  form a tuned antenna  149  that is connected to the PIN diode switch  141 . 
         [0107]      FIG. 15  shows an example circuit for an antenna incorporating several RF switches. PIN diode RF switches  151  and  152  are forward biased by inductors  153 , 154  and  155 , current limit resistor  156  and pull down transistor  157 . The diodes are reverse biased by pull up resistor  158  and voltage balancing resistors  159  and  1510  when transistor  157  is OFF. The tuned antenna consists of tuned circuit elements  1511  and  1512 . 
         [0108]      FIG. 16(   a ) shows yet another example circuit of an antenna incorporating several RF switches. The circuit shown in  FIG. 16  has double the reverse bias across each PIN diode switch  161  and  162  by applying the reverse bias at the centre of the antenna through pull up resistor  163 . In this way the reverse bias is divided between fewer series connected diodes The PIN diodes forward bias current is input from both ends of the antenna through inductors  164  and  165 , current limiting or balancing resistors  166  and  167 , inductors  168  and  169  and pull down transistor  1610 . The tuned antenna consists of tuned circuit elements  1611 ,  1612  and  1613 . 
         [0109]      FIG. 16(   b ) shows yet another example of an antenna incorporating several RF switches  161 . Each PIN diode switch is individually connected to the reverse bias through isolating inductors  163  and resistor  164 . When transistor  165  is OFF the reverse bias voltage is applied across each diode by pull up resistor  166 . When transistor  165  is ON the diodes are forward biased. Current limiting or balancing resistors  166  ensure that each diode draws an equal current. 
         [0110]    As would be appreciated by those skilled in the art, combinations of the biasing methods shown and numbers of diodes can be used depending upon the characteristics of the antenna. If there is a high inductive coupling from adjacent or overlapping antennas then a higher reverse bias voltages per PIN diode will be required to counteract the induced voltage. If there is a high stray capacitance between adjacent or overlapping antenna coils then more PIN diodes will be required to open the coils in more places. The shorter the open coil lengths are the lower the stray capacitance of each length becomes. 
         [0111]    It would also be understood that various of the embodiments disclosed herein are possible by variations to and/or various combinations of the embodiments, as might be required. 
         [0112]      FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ) and  19 ( c ) show various antenna arrays. For clarity purposes each antenna is shown as only one turn where as they may consist of multiple turns. Multiple turn coils have the advantages of producing a stronger field and receiving a stronger transponder reply signal as the conductors are connected in series. The conductors are suitably interconnected, but the connections are not shown as any suitable manner of coupling to a source of power and/or communications can be implemented. 
         [0113]    The conductors and/or the antennas may be placed in an overlapping position with respect to each other. The amount of the overlap may be anywhere between greater than 0% and less than 100%. 
         [0114]      FIG. 17(   a ) shows an array of antennas  171 ,  172 ,  173 ,  174  suitable for generating a sequentially switched interrogation field in at least one dimension. The antennas are arranged to overlap sufficiently to ensure reliable field strengths in the Z direction where the Z direction is normal to the plane of the antennas. The cross sectional view through a 1 -a 2  shows the magnetic field directions  178  and  179  for the two antennas  171  and  172  respectively. A tag oriented to be powered in the Z direction is shown in positions  175  and  176  near the centre of the antennas  171  and  172  and in position  177  in the overlapping region. There is a reliable field strength in the Z direction for all three positions  175 ,  176  and  177 , The overlap ensures that there is a reliable field in the Z direction regardless of the tag position above (or below) the antenna array. 
         [0115]    The antenna array of  FIG. 17(   a ) is sequentially switched in order to generate the interrogation field in at least one dimension. Due to the antennas close proximity there will be high levels of inductive and capacitive parasitic coupling. Capacitive parasitic coupling results in parasitic currents flowing through the stray capacitance from the active antenna into the not active antennas. Inductive parasitic coupling causes voltages to be induced in the not active antennas and these voltages result in parasitic currents flowing in the not active antennas. The parasitic currents and voltages increase the losses of the active antenna, may detune the active antenna, may generate harmonics in circuits connected to the not active antennas and may distort the field direction. These parasitic coupling effects are undesirable. If each antenna incorporates individually or a combination of RF switches as shown in  FIGS. 14 ,  15 ,  16 ( a ) and  16 ( b ) then the antennas array can be sequentially switched and the effects of the parasitic mutual coupling between the antennas (both capacitive and inductive) can be eliminated or minimised. 
         [0116]    The antenna array of  FIG. 17(   a ) has 4 antennas  171 ,  172 ,  173 ,  174  and would require 4 connecting cables to a reader. If the number of antennas in the array is increased to increase the size of the array then an additional connecting cable will be required for each additional antenna. The ever enlarging bundle of cables represents an additional cost and an installation difficulty. 
         [0117]      FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  show example circuits suitable for RF switch control which are controlled using a single cable for conveying bidirectional RF signals and bidirectional data using a DC power signal. By incorporating RF, switches directly into the antennas of the antenna array shown in  FIG. 17(   a ) and controlling the antenna array with a single cable for conveying bidirectional RF signals and bidirectional data using a DC power signal, the bundle of connecting cables can be replaced with a single cable. 
         [0118]      FIG. 17(   b ) shows an antenna array suitable for generating a sequentially switched interrogation field in at least one dimension where an RF switch control circuit  1714  as shown for example in  FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  has been included. The switch control circuit  1714  is controlled using a single cable  1715  for conveying bidirectional RF signals and bidirectional data using a DC power signal and each antenna  1710 ,  1711 ,  1712 ,  1713  incorporates individually or a combination of RF switches as shown for example in  FIGS. 14 ,  16 ,  16 ( a ) and  16 ( b ). The antenna array has the same antenna pattern as shown in  FIG. 17(   a ) to ensure reliable field strengths in the Z direction where the Z direction is normal to the plane of the antennas. Only one cable is required to connect to the antenna array which greatly reduces the cost and complexity of installation. Furthermore each port of a multi-port reader can now control one array where each array can consist of many antenna elements greatly increasing the number of antennas connected to a single reader and reducing the total number of readers required in an installation. 
         [0119]    The antennas of the sequentially switched antenna array of  FIG. 17(   b ) are significantly smaller than the overall size of the array. The emission of radiation from an electrically small loop is proportional to the magnetic moment of the antenna coil. An electrically small loop is a loop with dimensions less than 1/10 of the operating frequency free space wavelength and the magnetic moment of a coil is the product of coil area times the number of turns and the coil current. By using many small antennas with a cumulative area equal to the total array area to replace one large antenna equal to the array area the emission of radiation is significantly reduced. 
         [0120]      FIG. 18(   a ) shows an array of antennas  181 ,  182 ,  183  suitable for generating a sequentially switched interrogation field in at least two dimensions. The antennas are arranged to overlap sufficiently to ensure reliable field strengths in the X and Z directions where the X direction is in the plane of the antenna array and the Z direction is normal to the plane of the antennas. A preferable overlapping is one that achieves a uniform antenna conductor spacing. The cross sectional view through a 3 -a 4  shows the magnetic field directions  184  and  185  for the two antennas  181  and  182  respectively. A tag oriented to be powered in the X and Z directions is shown in positions  186  and  187  respectively. As the antennas array is sequentially switched there is a reliable field strength in the and Z directions above the antenna array regardless of the tag position above (or below) the antenna array. 
         [0121]    The antenna array of  FIG. 18(   a ) has 3 antennas  181 ,  182 ,  183  and would require 3 connecting cables to a reader. If the number of antennas in the array is increased to increase the size of the array then an additional connecting cable will be required for each additional antenna. The ever enlarging bundle of cables represents an additional cost and an installation difficulty. 
         [0122]      FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  show example circuits suitable for RF switch control which are controlled using a single cable for conveying bidirectional. RF signals and bidirectional data using a DC power signal. By incorporating RF switches directly into the antennas and RF switch control circuits, that use a single cable for conveying bidirectional RF signals and bidirectional data using a DC power signal, directly into the antenna array the bundle of connecting cables can be replaced with a single cable. 
         [0123]      FIG. 18(   b ) shows an antenna array suitable for generating a sequentially switched interrogation field in at least two dimensions where an RF switch control circuit  188  as shown for example in  FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  has been included. The switch control circuit  188  is controlled using a single cable  1812  for conveying bidirectional RF signals and bidirectional data using a DC power signal and each antenna  189 ,  1810  and  1811  incorporates individually or a combination of RF switches as shown for example in  FIGS. 14 ,  15 ,  16 ( a ) and  16 ( b ). The antenna array has the same antenna pattern as shown in  FIG. 18(   a ) to ensure reliable field strengths in the X and Z directions where the X direction is in the plane of the antenna array and the Z direction is normal to the plane of the antennas. Only one cable is required to connect to the antenna array which greatly reduces the cost and complexity of installation. Furthermore each port of a multi-port reader can now control one array where each array can consist of many antenna elements greatly increasing the total number of antennas connected to a single reader and reducing the number of readers required in an installation. 
         [0124]      FIGS. 19(   a ),  19 ( b ) and  19 ( c ) illustrates how two panels of parallel sequentially switched conductors when placed parallel to each other with the conductors orthogonally orientated will produce a three dimensional field. These panels are constructed in accordance with the principles for constructing or operating sequentially switched parallel conductor explained above and shown in  FIGS. 18(   a ) and  18 ( b ). For  FIGS. 19(   a ),  19 ( b ) and  19 ( c ) the X, Y and Z directions are; X horizontal left to right on the page, Y vertical up and down on the page, and Z in the third dimension coming directly out of the page surface. 
         [0125]    The antenna panel  191  shown in  FIG. 19(   a ) has parallel conductors  192  arranged in a horizontal direction and produced a field in the Y direction and in the Z direction. The conductors are suitably interconnected, but the connections are not shown as any suitable manner of coupling to a source of power and/or communications can be implemented. 
         [0126]    The antenna panel  193  shown in  FIG. 19(   b ) has parallel conductors  194  arranged in a vertical direction and produced a field in the X direction and in the Z direction. The conductors are suitably interconnected, but the connections are not shown as any suitable manner of coupling to a source of power and/or communications can be implemented. 
         [0127]    Due to their planar construction the panels  191  and  193  can be place onto of each other as shown in  FIG. 19(   c ). The panels are shown offset for clarity however this is not required for operation and the panels can be stacked directly on top of each other. The conductors in this composite panel are now sequentially switched such that only one coil or conductor set is active at a time. The composite panel will produce a field in the X, Y and Z directions as it is sequentially switched. 
         [0128]    The antenna array of  FIG. 19(   c ) would require a connecting cable between a reader and the antenna for each antenna. If the number of antennas in the array is increased to increase the size of the array then an additional connecting cable will be required for each additional antenna. The ever enlarging bundle of cables represents an additional cost and an installation difficulty. 
         [0129]      FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  show example circuits suitable for RF switch control which are controlled using a single cable for conveying bidirectional RF signals and bidirectional data using a DC power signal. By incorporating RF switches directly into the antennas and RF switch control circuits, that use a single cable for conveying bidirectional RF signals and bidirectional data using a DC power signal, directly into the antenna array the bundle of connecting cables can be replaced with a single cable. 
         [0130]      FIG. 19(   d ) shows, an antenna array  195  suitable for generating a sequentially switched interrogation field in three dimensions where an RF switch control circuit  196  as shown for example in  FIGS. 10(   a ),  10 ( b ),  11 ,  12  and  13  has been included. The array is a composite panel of orthogonally arranged conductors as shown in  FIG. 19(   c ). The panels are shown offset in  FIG. 19(   c ) for clarity however this is not required for operation and the panels can be stacked directly on top of each other as shown in  FIG. 19(   d ). The switch control circuit  196  is controlled using a single cable  197  for conveying bidirectional RF signals and bidirectional data using a DC power signal and each antenna in the array  195  incorporates individually or a combination of RF switches as shown in  FIGS. 14 ,  15 ,  16 ( a ) and  16 ( b ). The antenna array  195  has the same antenna pattern as shown in  FIG. 19(   c ) to ensure reliable field strengths in the X, Y and Z directions. Only one cable is required to connect to the antenna array which greatly reduces the cost and complexity of installation. Furthermore each port of a multi-port reader can now control one array where each array can consist of many antenna elements greatly increasing the total number of antennas connected to a single reader and reducing the number of readers required in an installation. 
         [0131]      FIGS. 20(   a ) and  20 ( b ) show an array of antennas suitable for generating a sequentially switched interrogation field where the array is connected to a reader  201  by a single cable  202 . 
         [0132]      FIG. 20(   a ) shows an array  203  where the cable entry  204  is from the side of the array. The antenna array has been encapsulated in a protection sleeve  205  manufactured, for example, from a light durable plastic such a “Firmex” an expanded PVC foam. Firmex is light and can be precisely machined to accommodate the antenna array and array components. A side entry antenna array is suited to applications where both the array and the connecting cable are to be placed on a flat surface. 
         [0133]      FIG. 20(   b ) shows an array  206  where the cable entry  207  is from the surface of the array. The antenna array has been encapsulated in a protection sleeve  208  manufactured, for example, from a light durable plastic such a “Firmex” an expanded PVC foam. Firmex is light and can be precisely machined to accommodate the antenna array and array components. A surface entry antenna array is suited to applications where there is to be placed on a flat surface and the connecting cable is required to penetrate the mounting surface. This is applicable for example to table of wall fixings where the reader is located below the table or behind the wall. 
         [0134]      FIG. 21  shows an application for the invention where the invention is included in a shelving system  211 . The invention can be included in the shelves  212  and/or the side walls  213  and/or the back wall  214  and/or front door  215  of the shelving cabinet. The invention can provide two or three dimensional reading depending upon the placement of and direction of the conductors use. The invention can be made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). 
         [0135]      FIG. 22  shows another application for the invention where the invention is used to read closely stacked gem or jewellery transponders  221 . Each gem or jewel is placed in a small envelope  222  that is place closely stacked in a transport and storage box  223 . A transponder  221  is also placed in each envelope and identifies the gem or jewel. The transponder may also be programmed with information about the gem/jewel and/or be programmed with transport information. The contents of the box can be quickly read for stock take or security purposes by placing in on a panel  224  made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). 
         [0136]      FIG. 23  shows still a further application for the invention where the invention is used to read closely stacked gaming tokens  231  which include an embedded transponder  232 . Each token is placed closely stacked in a croupier&#39;s tray  233  for gaming, transport and storage. The transponder  232  identifies the token and may also be programmed with information about the token and/or owner of the token and/or transport information. The contents of the croupiers box  233  can be quickly read for operational, stock take or security purposes by placing in on a panel  234  made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). 
         [0137]      FIG. 24  shows still a further application for the invention where the invention is used to read closely stacked gaming tokens  241  which include an embedded transponder  242 . Each token is placed closely stacked in a vertical column  241  on table or tray  243  for gaming, transport or storage. The transponder  242  identifies the token and may also be programmed with information about the token and/or owner of the token and/or transport information. All of the tokens placed on the antenna  244  can be quickly read for operational, stock take or security purposes. The panel  244  being made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). This is a particularly advantageous interrogator antenna for roulette tables and mass storage systems for gaming tokens. 
         [0138]      FIG. 25  shows still a further application for the invention where the invention is used to read closely stacked document pages  251  which include an attached or embedded transponder  252 . Each page is placed closely stacked in a vertical column  251  on a tray  253  for processing, transport or storage. The transponder  252  identifies the document page and may also be programmed with information about the page and/or owner of the page and/or transport information. All of the pages placed on the antenna  244  can be quickly read for operational, stock take or security purposes. The panel  244  being made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). This is a particularly advantageous interrogator antenna for offices and archive storage systems for documents. 
         [0139]      FIG. 26  shows still a further application for the invention where the invention is used to read displayed items of substantial value such as gems, jewellery or sunglasses  261  which include an embedded or attached transponder  262 . Each displayed item is placed on a display tray  263  for display, sale, transport, stock take or storage. The transponder  262  identifies the display item  261  and may also be programmed with information about the item and/or owner of the item and/or value of the item and/or transport information. All of the display items placed on the antenna  264  can be quickly read for operational, stock take or security purposes. The panel  264  being made according to either or any of  FIGS. 17(   a ),  17 ( b ),  18 ( a ),  18 ( b ),  19 ( a ),  19 ( b ),  19 ( c ) and  19 ( d ). This is a particularly advantageous interrogator antenna for retail stores where items of value, such as gems, jewellery or sunglasses for example, are displayed for sale. 
         [0140]    With regard to  FIG. 27 , a communication method may be used between a 1 st  &amp; 2 nd  device in which the 1 st  device transmits a control or data signal to the 2 nd  device using an RF signal which is modulated and/or switched. A corresponding receiving and/or demodulation circuitry is then provided in the 2 nd  device in order to receive the control or data signals. In one form, the RE signal is switched off for short periods of time, and the envelope of the RF signal is detected by a diode peak detection circuit.  FIG. 27  illustrates two alternative communication methods, either of which may be used. In a first method, a data signal  2701  is imposed on a DC power  2703 , in which case, the signal  2701  is used (for example to clock the counter) via the DC peak detector  2702 . In a second method, the data signal  2701  may be imposed on an AC signal  2704 , in which case the signal  2701  is detected via AC peak detector  2705 . 
         [0141]    With regard to  FIG. 28 , a 1 st  device  2813  is connected using a single cable  2811  to a 2 nd  device  2814 . A communication method may be used between a 1 st  &amp; 2 nd  device in which the 1 st  device transmits a control or data signal  2810  to the 2 nd  device using a frequency for the control or data signal that is not the same as the frequency of the bidirectional RF signal  2812 . The control or data signal is modulated using an RF modem  288  in the 1 st  device. A corresponding RF modem  289  is then provided in the 2 nd  device to receive and output the control or data signal  2810 . In one form, the RE modems are low cost short range modems compliant with an IEEE 802.15.4 ZigBee™. Bidirectional data may be exchanged between the modems  288  and  289 . Power  283  for the 2 nd  device is provided by the DC voltage source  280  and passes through the low pass filters formed by inductors  281  and  282 . The RF signal  2812  passes through the band pass filters  284  and  285 . The RF modulated control or data signal  2815  is passed through the high pass filters  286  and  287 . 
         [0142]    While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth. 
         [0143]    As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive. 
         [0144]    Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures. For example, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface to secure wooden parts together, in the environment of fastening wooden parts, a nail and a screw are equivalent structures. 
         [0145]    It should be noted that where the terms “server”, “secure server” or similar terms are used herein, a communication device is described that may be used in a communication system, unless the context otherwise requires, and should not be construed to limit the present invention to any particular communication device type. Thus, a communication device may include, without limitation, a bridge, router, bridge-router (router), switch, node, or other communication device, which may or may not be secure. 
         [0146]    It should also be noted that where a flowchart is used herein to demonstrate various aspects of the invention, it should not be construed to limit the present invention to any particular logic flow or logic implementation. The described logic may be partitioned into different logic blocks (e.g., programs, modules, functions, or subroutines) without changing the overall results or otherwise departing from the true scope of the invention. Often, logic elements may be added, modified, omitted, performed in a different order, or implemented using different logic constructs (e.g., logic gates, looping primitives, conditional logic, and other logic constructs) without changing the overall results or otherwise departing from the true scope of the invention. 
         [0147]    Various embodiments of the invention may be embodied in many different forms, including computer program logic for use with a processor (e.g., a microprocessor, microcontroller, digital signal processor, or general purpose computer), programmable logic for use with a programmable logic device (e.g., a Field Programmable Gate Array (FPGA) or other PLD), discrete components, integrated circuitry (e.g., an Application Specific Integrated Circuit (ASIC)), or any other means including any combination thereof. In an exemplary embodiment of the present invention, predominantly all of the communication between users and the server is implemented as a set of computer program instructions that is converted into a computer executable form, stored as such in a computer readable medium, and executed by a microprocessor under the control of an operating system. 
         [0148]    Computer program logic implementing all or part of the functionality where described herein may be embodied in various forms, including a source code form, a computer executable form, and various intermediate forms (e.g., forms generated by an assembler, compiler, linker, or locator). Source code may include a series of computer program instructions implemented in any of various programming languages (e.g., an object code, an assembly language, or a high-level language such as Fortran, C, C++, JAVA, or HTML) for use with various operating systems or operating environments. The source code may define and use various data structures and communication messages. The source code may be in a computer executable form (e.g., via an interpreter), or the source code may be converted (e.g., via a translator, assembler, or compiler) into a computer executable form. 
         [0149]    The computer program may be fixed in any form (e.g., source code form, computer executable form, or an intermediate form) either permanently or transitorily in a tangible storage medium, such as a semiconductor memory device (eg, a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a magnetic memory device (e.g., a diskette or fixed disk), an optical memory device (e.g., a CD-ROM or DVD-ROM), a PC card (e.g., PCMCIA card), or other memory device. The computer program may be fixed in any form in a signal that is transmittable to a computer using any of various communication technologies, including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless technologies (e.g., Bluetooth), networking technologies, and inter-networking technologies. The computer program may be distributed in any form as a removable storage medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the communication system (e.g., the Internet or World Wide Web). 
         [0150]    Hardware logic (including programmable logic for use with a programmable logic device) implementing all or part of the functionality where described herein may be designed using traditional manual methods, or may be designed, captured, simulated, or documented electronically using various tools, such as Computer Aided Design (CAD), a hardware description language (e.g., VHDL or AHDL), or a PLD programming language (e.g., PALASM, ABEL, or CUPL). 
         [0151]    Programmable logic may be fixed either permanently or transitorily in a tangible storage medium, such as a semiconductor memory device (e.g., a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a magnetic memory device (e.g., a diskette or fixed disk), an optical memory device (e.g., a CD-ROM or DVD-ROM), or other memory device. The programmable logic may be fixed in a signal that is transmittable to a computer using any of various communication technologies, including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless technologies (e.g., Bluetooth), networking technologies, and internetworking technologies. The programmable logic may be distributed as a removable storage medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the communication system (e.g., the Internet or World Wide Web). 
         [0152]    “Comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.” Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.