Abstract:
An antenna for a transceiver. The antenna is switchable between a receive and a transmit mode. In receive mode, the antenna is configured to provide increased sensitivity for improved inductive pickup of signals. In transmit mode, the antenna is configured to provide efficient power output without undue losses. The antenna coil comprises a plurality of conductor bundles. In receive mode, the conductor bundles in series to increase the number of effective turns in the antenna coil and thereby increase the inductive pickup of the coil for receiving signals. In transmit mode, the conductor bundles are configured in parallel. The parallel configuration of the conductor bundles reduces the AC and DC resistance of the antenna coil, and therefore the power loss, to allow the antenna to be driven efficiently to transmit signals.

Description:
FIELD OF THE INVENTION 
     The present relates to transceivers, and more particularly to a transceiver having an antenna switchable between a receive mode and a transmit mode. 
     BACKGROUND OF THE INVENTION 
     Transceivers comprise a radio transmitter and a radio receiver combined in a single unit with a switch to permit both transmission and reception of signals. In designing a transceiver, it is highly desirable to utilize a single antenna for sending and receiving. However, using the same antenna for transmitting and receiving presents a number of problems. 
     The principle problem for a single antenna design is the trade-off between sufficient sensitivity for receiving signals and maintaining manageable voltage levels and losses for transmitting. In order to provide sufficient sensitivity for receiving signals, it is desirable to increase the number of turns (wire) in the antenna. While increasing the number of turns improves the sensitivity for reception, higher voltage levels are required to drive the additional turns when the antenna is used for the transmission of signals. There are also the associated electrical losses in the turns of the coil for the antenna. Since most transceivers are battery powered, power needs and losses are an important design consideration. 
     Accordingly, there remains a need for antenna configuration suitable for a transceiver which overcomes these problems. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides an antenna for a transceiver which is switchable between a receive and a transmit mode. In receive mode, the antenna is configured to provide increased sensitivity for improved inductive pickup of signals that are transmitted via either magnetic fields or electromagnetic waves, such as radio signals. In transmit mode, the antenna is configured to provide efficient power output without undue losses. 
     According to one aspect of the invention, the antenna is arranged using Litz-type wire. Litz wire comprises a plurality of bunched strands of fine wire. In transmit mode, all of the bunched strands are switched into a parallel configuration. In receive mode, all of the bunched strands are switched into a series configuration. In transmit mode, the parallel configuration has the effect of reducing proximity effect and power losses, thereby increasing battery life for the transceiver. In receive mode, the series configuration of the bunched wire strands effectively increases the number of turns which in turn improves the sensitivity of the transceiver by allowing more inductive pickup of signal. 
     In a first aspect, the present invention provides an antenna coil for a transceiver having a receiver module for receiving signals and a transmitter module for transmitting signals, the antenna coil comprises: (a) a plurality of conductors, each of the conductors having a first end and a second end; (b) a switch mechanism for coupling the conductors in parallel for operation in transmit mode, and the switch including an input port for connecting the first ends of the conductors to a first output terminal on the transmit module and second input port for connecting the second ends of the conductors to a second output terminal on the transmit module, the first and second output terminals forming an output port for the transmit module; (c) a switch mechanism for coupling the conductors in series for operation in receive mode, and the switch including a first port for connecting the first end of one of the conductors to a first input terminal on the receive module and a second port for connecting the second end of another of the conductors to a second input terminal on the receive module, the first and second input terminals forming an input port for the receive module; (d) a control mechanism for switching the switch mechanism between the receive mode and transmit mode of operation. 
     In a second aspect, the present invention provides an antenna coil for a transceiver, the transceiver being operable in a receive mode and a transmit mode, and the transceiver includes a receiver module for receiving signals in the receive mode and a transmitter module for transmitting signals in the transmit mode, the antenna coil comprises. (a) at least two conductors, each of the conductors having a first end and a second end; (b) a switching module having at least two first switch inputs, at least two second switch inputs, each of the first switch inputs being coupled to one of the first ends of each of the conductors, and each of the second switch inputs being coupled to one of the second ends of each of the conductors; (c) the switching module including at least two receive switch output ports and at least two receive switch input ports, and the switching module including at least two transmit switch input ports and at least two transmit switch output ports; (d) in the receive mode of operation, the first receive switch output is coupled to a first input terminal in the receiver module and the second receive switch output is coupled to a second input terminal in the receiver module, the second receive switch output port is coupled to the first receive switch input port, so that the conductors are coupled in series; (e) in the transmit mode of operation, the first and the second transmit switch input ports are coupled to a first output terminal in the transmit module, and the first and the second transmit switch output ports are coupled to a second output terminal in the transmit module, so that the conductors are coupled in parallel to the first and the second output terminals in the transmit module. 
     In yet another aspect, the present invention provides, a transceiver operable in a receive mode for receiving signals and operable in a transmit mode for transmitting signals, the transceiver comprises: (a) a receive module; (b) a transmit module; (c) a controller for selectively enabling the receive module to receive incoming radio signals to the transceiver, and for selectively enabling the transmit module to transmit outgoing signals from the transceiver; (d) an antenna coil, the antenna coil includes, (i) a plurality of conductors, each of the conductors having a first end and a second end; (ii) a switch mechanism for coupling the conductors in parallel for operation in the transmit mode, and the switch including an input port for connecting the first ends of the conductors to a first output terminal on the transmit module and second input port for connecting the second ends of the conductors to a second output terminal on the transmit module, the first and second output terminals forming an output port for the transmit module; (iii) a switch mechanism for coupling the conductors in series for operation in receive mode, and the switch including a first port for connecting the first end of one of the conductors to a first input terminal on the receive module and a second port for connecting the second end of another of the conductors to a second input terminal on the receive module, the first and second input terminals forming an input port for the receive module; (iv) a control mechanism for switching the switch mechanism between the receive mode and transmit mode of operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made to the accompanying drawings which show, by way of example, a preferred embodiment of the present invention, and in which: 
     FIG. 1 shows in schematic form a transceiver and a switchable antenna according to the present invention; 
     FIG. 2 shows in schematic form the switchable antenna according to the present invention configured for transmit mode; and 
     FIG. 3 shows in schematic form the switchable antenna according to the present invention configured for receive mode. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is first made to FIG. 1 which shows in schematic form a transceiver  10  and a switchable antenna coil  12  according to the present invention. As shown in FIG. 1, the transceiver  10  comprises a transmitter  14  and a receiver  16 . In known fashion, the transmitter  14  and the receiver  16  are combined into a single unit in the transceiver  10  to permit both transmission and reception of signals. In the context of the present invention, the term signal means a signal that is transmitted via electromagnetic waves, for example radio signals, or a signal that is transmitted via a magnetic field. Accordingly, the transceiver  10  may be implemented for the transmission and reception of radio signals. Further implementation details for the transmitter  14  and the receiver  16  in the context of the transceiver  10  will be within the understanding of the those skilled in the art. 
     As shown in FIG. 1, the antenna  12  according to the present invention comprises a series of bundles  20 , shown individually as  20   a,    20   b , . . . ,  20   s −1,  20   s.  Each bundle  20  has input end  21 , shown individually as  21   a , 21   b , . . .  21   s −1,  21   s,  and an output end  22 , shown individually as  22   a,    22   b , . . .  22   s −1,  22   s,  in FIG.  1 . Each bundle  20  comprises one or more strands of wire  24 , shown individually as  24   a,    24   b , . . .  24   n −1,  24   n,  for the first bundle  20   a.  In the preferred embodiment, the antenna coil  12  is conveniently implemented using known Litz-type wire. Litz-type wire comprises a series of bundles, with each bundle having one or more strands of wire. 
     As also shown in FIG. 1, the transceiver  10  includes a switching module  30  which couples the antenna coil  12  to the transmitter  14  and to the receiver  16 . The switching module  30  switches the antenna coil  12  between the transmit and receive modes. The switching module  30  includes a switching element  32  for each of the input ends  21  of the bundles  20 . The switching elements  32  are shown individually as  32   a,    32   b , . . .  32   s  in FIG.  1 . Similarly, the switching module  30  includes a switching element  34  for each of the output ends  22  of the bundles. The switching elements  34  are shown individually as  34   a , . . .  34   s −1,  34   s  in FIG.  1 . Each pair of switching elements  32 ,  34  couples the associated bundle  20  in the antenna coil  12  to the transceiver  10  and switches the bundle  20  between the transmitter  14  and the receiver  16 , in the transmit and receive modes of operation respectively as will be described in more detail below. The switching elements  32 ,  34  are switched between the transmit and receive modes through a switching control signal  36  which is applied at a control port  38 . The control signal  36  to switch between transmit and receive modes may be generated in any number of ways in the transceiver  10  as will be familiar to one skilled in the art. 
     Reference is next made to FIG. 2, which shows the configuration of the antenna coil  12  in the transmit mode of operation, ie. the transceiver  10  uses the antenna coil  12  to transmit signals. In transmit mode, the bundles  20  in the antenna  12  are connected in parallel to a transmit output port  15  on the transmitter  14  through the switching module  30 . The input ends  21  of the bundles  20  are connected to respective input switching elements  32 . Each of the input switching elements  32  includes an input port  38 , a first output port  40 , and a second output port  41 . In FIG. 2, the input ports  38 , the first output ports  40  and the second output ports  41 , are shown individually as  38   a,    38   b , . . .  38   s,    40   a,    40   b , . . .  40   s,  and  41   a,    41   b , . . .  41   s,  respectively. Similarly, the output ends  22  of the bundles  20  are connected to respective switching elements  34  in the switching module  30 . As shown, each of the output switching elements  34  includes an input port  39 , a first output port  42 , and a second output port  43 . In FIG. 2, the input ports  39 , the first output ports  42  and the second output ports  43 , are shown individually as  39   a,    39   b , . . .  39   s,    42   a,    42   b , . . .  42   s,  and  43   a,    43   b , . . .  43   s,  respectively. In transmit mode, the switching elements  32  are switched so that the input ends  21  of the bundles  20  are coupled together, and similarly, the switching elements  34  are switched so that the output ends  22  of the bundles the bundles  20  are coupled together. i.e. the input end  21  of each of the bundles  20  is connected together at a first terminal or node  44  through the second output port  41  of the input switching element  32 , and the output end  22  of each of the bundles  20  is connected together at a second terminal or node  46  through the second output port  43  of the output switching elements  34 . (The terminals  44  and  46  form the output port  15  for the transmit module  14 .) This switched arrangement results in the bundles  20  being effectively connected in parallel. The transmitter  14  is coupled to connected input ends  21  of the bundles  20  at the node  44  and the connected output ends  22  of the bundles  20  at the node  46 . The resulting parallel configuration of the bundles  20  in the antenna coil  12  gives the transmitter  14  an increased number of wire strands  24  per turn arranged as Litz-type wire. Advantageously, the increased number of wire strands  24  per turn arranged as Litz-type wire, reduces the AC resistance, and therefore power loss resulting in efficient operation of the antenna coil  12 . 
     Reference is next made to FIG. 3, which shows the configuration of the antenna coil  12  in the receive mode of operation, i.e. the transceiver utilizes the antenna coil  12  for receiving signals. As shown in FIG. 3, in receive mode the bundles  20  are connected end-to-end in series. This series arrangement of the bundles  20  effectively increases the number of turns on the antenna by the number of bundles, i.e. S. As shown in FIG. 3, the input end  21   a  of the first bundle  20   a  is coupled to the radio receiver  16  in the transceiver  10  through the first output port  40   a  of the switching element  32   a  at a first input terminal  48 , and the output end  22   s  of the last bundle  22   s  is coupled to a second input terminal  50  on the receiver  16  through the first output port  42   s  of the last switching element  34   s.  The first  48  and second  50  terminals form an input terminal  17  for the receiver module  16  for receiving the signals coupled by the antenna coil  12 . The remaining bundles  20  are connected end-to-end in series. As shown, the input end  21   b  of the second bundle  20   b  is coupled to the output end  22   a  of the first bundle  20   a  through the switching elements  32   b  and  34   a,  and the input end  21   s  of the last bundle  20   s  is coupled to the output end  22   s −1 of the second last bundle  20   s −1 through the switching elements  32   s  and  34   s −1. By coupling the bundles  20  in series, the effective number of turns of the antenna coil  12  is increased. The increased number of turns results in better sensitivity of the antenna coil  12  which produces a higher level output for a given magnetic field strength input signal. If each one of the bundles  20  comprises more than one strand  24 , then the connection of the individual strands  24  in a bundle  20  further reduces AC resistance and power loss in the antenna coil  12  in receive mode. Advantageously, the antenna coil  12  operates more efficiently allowing a higher output signal level for a given magnetic field than a conventional antenna with equal turns of a single wire. 
     The performance of the antenna coil  12  according to the present invention is now described in the context of the following example. 
     In this example, the characteristics of the antenna coil  12  are compared to a conventional antenna transmit coil formed of 120 turns of solid wire with an AWG of #10 requiring 102 Watts of power to produce a drive current of approximately 10 A through the coil to yield 110 A-m z . In receive mode, the 120 turns of wire yield the following parameters 2.87 mH, 59 Ohms, Q=91, and emf=0.019 mV at 1 pT and 3 kHz. As will now be described, the power requirement drops with an antenna coil  12  according to the present invention. 
     Next, an antenna coil  12  according to the present invention comprising a Litz-type wire with 120 turns and having 51 bundles  20  (i.e. s=51) is considered. Each bundle comprises a single wire strand  24  having a wire gauge (AWG) of #27. In transmit mode, the 51 bundles  20  (or strands  24 ) are coupled in parallel, and the current in each bundle  20  is approximately 196 mA (i.e. 10 A/51). Because the current magnitudes are not high, the switching elements  32 ,  34  (FIG. 1) may be implemented using small switches. In receive mode, the 51 bundles  20  are coupled in series end-to-end as described above and the effective number of turns of the coil is 6120 (i.e N=120×51) of AWG #27. On a first approximation, the 6120 turns yields the following characteristics: Inductance=7.5 H, DC resistance=1500 ohms, Q=98, emf=1 mV at 1 pT and 3 kHz. It until be appreciated that the AC resistance is not accounted for in this approximation, but would be considerable. 
     Next, the antenna coil  12  is considered with the 51 bundles  20  (of the 120 turns of Litz-type wire) being arranged into 10 bunches with 5 wire strands each (and one bunch having 6 wire strands). i.e. 51/5=10. The effective wire gauge (AWG) for each bundle of 5 strands is #20. Each switch  32 ,  34  (FIG.  1 ), in turn, must handle 10 A/10=1 A of current in transmit mode. In receive mode, the bundles  20  are coupled in series end-to-end resulting in an antenna coil  12  with 1200 turns (i.e. N=10×120), which yields the following characteristics: Inductance=289 mH, DC resistance=56 Ohms, Q=97, and EMF=0.2 mV at 1 pT and 3 kHz. Again AC resistance was not accounted for, but would be considerable. 
     It will be appreciated that for the antenna coil  12 , the inductance goes up by a factor of s 2 , the DC resistance also goes up by a factor s 2  (i.e. s times the resistance by s times the length), and the induced EMF goes up by a factor of s. 
     The following three experiments were conducted with an antenna formed as a single-layer  120  turn rectangular coil. In the first experiment, the antenna coil  12  is configured in receive mode according to the present invention with 51 bundles (i.e. s=51); in the second experiment, the antenna coil  12  is configured in receive mode with 10 bundles (i.e. s=10) according to the present invention; and in the third a conventional antenna comprising 120 turns of a single solid wire is utilized. 
     (1) Single-Layer Rectangular Antenna Coil ( 12 ) in Receive Mode 
     120 turns switched with 51 bundles (i.e. s=51) 
     Set centre frequency &amp; modulation shift frequency (Hz): 
     f 0 :=3000·Hz 
     Set parameters for antenna coil  12 : 
     N=6120 (i.e. total number of turns of wire on the coil) 
     AWG=27 (wire gauge) 
     w=7.125 in (width of rectangle) 
     h=20.375 in (height of rectangle) 
     I=13.5 in (length of rectangular coil) 
     Calculations: 
     area=0.093659 m 2  (i.e. w×h) 
     wirelength=8.54964.10 3  m (i.e. 2·(w+h)·N) 
     R=R_dc(AWG,wirelength, 20 )skin_effect(f 0 ,wr(AWG)+Rdson then, R=1.44368·10 3 ° Ω 
     L=Lslrc(w,h,I,2·wr(AWG),N) then, L=7.541465·10 6 ° μH 
     Results for receive mode: 
     N=6.12 10 3  f 0 =3000° Hz 
     L=7541.465° mH 
     R=1443.68004° Ω Weu(wirelength,AWG)=7.760872° kg 
     Weu(wirelength,AWG)=17.109793° lb 
     Q(f 0 ,L,R)=98.465902 
     R_dc(AWG,wirelength, 20 )=1443.64° Ω 
     Vemf(10 −12 T,N,f 0 ,area,Q(f 0 ,L,R))=1.063869° mV 
     (2) Single-Layer Rectangular Antenna Coil ( 12 ) with 10 Bundles 
     120 turns switched with 10 bundles (i.e. s=10) 
     Set centre frequency &amp; modulation shift frequency (Hz): 
     f 0 =3000·Hz 
     Set parameters for antenna coil  12 : 
     N=1200 
     AWG=20 
     w=7.125·in 
     h=20.375·in 
     I=13.5·in 
     Calculations: 
     area=0.093559 m 2  (i.e. w×h) 
     wirelength=1.6764.10 3  m (i.e.2·(w+h)·N) 
     R=R_dc(AWG,wirelength, 20 )·skin_effect(f 0 ,wr(AWG)+Rdson then, R=55.879111° Ω 
     L=Lslrc(w,h,I,2·wr(AWG),N) then, L=0.289H 
     Results for transmit mode: 
     N=1.2·10 3  f 0 =3000° Hz 
     L=289.039° mH 
     R=55.879111° Ω Weu(wirelength,AWG)=7.71418° kg 
     Weu(wirelength,AWG)=17.006856° lb 
     Q(f 0 ,L,R)=97.500704 
     R_dc(AWG,wirelength, 20 )=55.839° Ω 
     (3) Conventional Single-Layer Rectangular Antenna Coil 
     120 turns single strand wire (i.e. s=1) 
     Set centre frequency &amp; modulation shift frequency (Hz): 
     f 0 =3000·Hz 
     Set coil parameters for conventional antenna: 
     N=120 
     AWG=10 
     w=7.125·in 
     h=20.375·in 
     I=13.5·in 
     Calculations: 
     area=0.093559 m 2  (i.e. w×h) 
     wirelength=167.64 m (i.e. 2·(w+h)·N) 
     R=R_dc(AWG,wirelength, 20 )·skin_effect (f 0 ,wr(AWG)+Rdson then, R=0.589195° Ω 
     L=Lslrc(w,h,I,2·wr(AWG),N) then, L=2.867349·10 5 ° μH 
     Set moment, or AT, or I: 
     M=area·I·N AT:=M·area −3  I=AT·N −1  then, M=110·A·m 2  AT=1.174472·10 3 A I=9.787269 A 
     Results for conventional antenna: 
     N=120 f 0 =3000° Hz Δf=100° Hz Vbat=100° V 
     I=9.787° A Vcoil(f 2 ,L,I)=537.801° V L=2.867° mH 
     AT=1.174472·10 3 ° A Vcoil(f 2 ,L,I)·{square root over (2)}=760.566° V 
     M=110·A·m 2    
     R=0.589195° Ω Weu(wirelength,AWG)=7.840801° kg 
     P(I,R)=56.44° W Weu(wirelength,AWG)=17.286008° lb 
     Q(f 0 ,L,R)=91.732399 
     R_dc(AWG,wirelength, 20 )=0.549° Ω 
     Vemf(10 −12 T,N,F 0 ,area,Q(f 0 ,L,R))=0.019434° mV 
     The parallel configuration of the bundles  20  (and strands  24 ) in transmit mode (FIG. 2) yields a low DC and AC resistance. A reasonable number of turns gives a voltage that is low enough to be dealt with conveniently. It will be understand that because there are numerous strands  24  of wire, the current in each strand  24  is 1/s times the total current, where s is the number of strands (FIG.  1 ). Advantageously, the small amount of current per strand  24  allows small, low current devices to be used for the switches  32 ,  34  in the switching module  30 , while at the same time still providing for a very large transmit current. Relays or even transistors or cross-point switches may be utilized for the switches  32  and  34 . It is further noted that the resistance of each switch  32 ,  34  is in parallel so that the total resistance of the switches  32  and  34  is given by R total =R switch /s. Where s is large, the resistance becomes insignificant. 
     For operation in receive mode, the number of turns in the antenna coil is effectively increased by s. This increase in the number of turns increases the inductance for the antenna coil  12 . Alternatively, several strands  24  may be switched together (instead of single strands). This configuration has the effect of lowering the AC and DC resistance, but the inductance of the antenna coil  12  is also lowered. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Certain adaptations and modifications of the invention will be obvious to those skilled in the art. Therefore, the presently discussed embodiments are considered to be illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein