Abstract:
An electrical control device for controlling the status of a controlled electrical device, the electrical control device comprising a power conducting semiconductor device for controlling the status of the controlled electrical device; a control circuit; a transmitter and/or receiver in communication with the control circuit; and an antenna coupled to the transmitter and/or receiver; the antenna adapted to receive a first signal at a specified frequency from a remote control device and/or transmit a second signal at a specified frequency to a remote control device; wherein the transmitter is operable to couple the first signal from the antenna to the control circuit for remotely controlling the controllably conductive device and/or couple the second signal from the control circuit for providing a status of said controlled electrical device, the antenna comprising a first loop of conductive material having a capacitance and an inductance; the capacitance and the inductance forming a circuit being resonant at the specified frequency; a second loop of conductive material having two ends adapted to be electrically coupled to a control circuit, the second loop being substantially only magnetically coupled to the first loop; the first and second loops each having a loop axis, the loop axes of the first and second loops being substantially parallel or coincident.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This is a divisional of U.S. patent application Ser. No. 10/873,033, filed Jun. 21, 2004 entitled COMPACT RADIO FREQUENCY TRANSMITTING AND RECEIVING ANTENNA AND CONTROL DEVICE EMPLOYING SAME, the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to antennas and in particular, to radio frequency antennas for transmitting and receiving radio frequency (RF) signals. Even more particularly, the present invention relates to a compact antenna, which is provided for use in connection with a radio frequency controlled lighting control system. In particular, the present invention relates to an antenna which is provided on a lighting control device, for example, a light dimmer, and which receives and/or transmits radio frequency signals for controlling a lamp and communicating status of the lamp, for example, on, off, and intensity level. The radio frequency signals are used to control from a remote master location the status of the lamp connected to the light dimmer and also to provide information back to the master location concerning the status of the controlled lamp. The device at the master location may also employ an antenna according to the invention.  
         [0003]     The invention also relates to a control device employing the antenna that can be mounted in a standard electrical wall box. In particular, the invention relates to a local electrical control device capable of remotely controlling one or more electric lamps and adapted to be mounted in a standard electrical wall box and receiving and transmitting signals via the antenna. The invention further relates to a master control device capable of remotely controlling one or more local electrical control devices and adapted to be mounted in a standard electrical wall box and employing the antenna to transmit to and receive signals from a local electrical control device which responds to the control signals from the master device.  
         [0004]     Although the present invention is directed to an antenna for use in a lighting control system, the antenna of the present invention can be applied to the communication of signals relating to the control and status of other devices, for example, communication equipment, motors, security systems, appliances, HVAC systems (heating, ventilating, and air conditioning) and other devices.  
         [0005]     The present invention is directed to an antenna of compact design which can be included within the lighting control device, for example a light dimmer, and which fits into a standard electrical wall box. The invention is also directed to a lighting control device itself, either a master or local (remote) unit. The invention is of particular use in a system which uses radio frequency signals to control the status of controlled electrical devices such as electric lamps. In such a system, the conventional manually controlled hard wired lighting control devices, for example, wall switches and dimmers, are replaced by control devices having a control circuit and an antenna according to the present invention. The system in which the antenna according to the present invention is used may thus be provided to enable an existing building lighting system (or other electrical/electronic devices) to be controlled remotely from various locations without requiring hard wiring of the building to incorporate the necessary control wiring to accomplish remote control of lighting fixtures or other devices. Accordingly, in a system in which the antenna of the present invention is used, the lighting control device, for example, a light dimmer which replaces the conventional light switch/dimmer, contains an antenna according to the present invention, the necessary actuators for accomplishing manual control of the lighting fixture, as well as a control circuit and RF circuit for allowing remote control via signals received and transmitted by the antenna of the lighting control device. The antenna and control device fit within a standard electrical wall box allowing the conventional lighting control device to be removed and replaced by the lighting control device according to the invention. Similarly, a master unit according to the invention having actuators thereon and an antenna for transmitting signals to the local control devices and receiving status signals from the local control device is also adapted according to one embodiment of the invention, to be disposed in a conventional electrical wall box.  
         [0006]     In accordance with the present invention, the antenna is of compact size such that it fits within the standard electric wall box together with the control device electronic circuitry and mechanical components and is a part of the electrical control device for controlling the lamp.  
         [0007]     In addition, although the control device employing the antenna of the present invention has been described in connection with its use in replacing conventional, non-radio frequency controlled lighting control devices, the present invention can also be employed in new construction so that the number of wires that need to be routed in the new construction can be reduced. Accordingly, in the system employing the present invention, it is not necessary to run control wires (only the electrical power wires need to be installed) to control the lighting system since the antenna of the present invention will and receive transmit radio frequency signals to accomplish this control.  
         [0008]     There is presently a system known in the prior art that allows for remote control of lamps without hard wiring the control wires to the lighting control devices. This known system is the Lutron Radio RA system in which lamps are controlled remotely by radio frequency signals. In the Radio RA system, each lighting control device, in addition to manual controls, has a transceiver and an antenna, which receives and transmits radio frequency signals from and to a master control unit. At the master control unit, the status of the various lamps in the building structure can be remotely controlled, that is, the on, off and intensity level status can be controlled from the master control unit by sending RF signals from the master device to the lighting control devices. In order to ensure that radio frequency signals are transmitted to and from all devices in the system, repeaters are employed as necessary. Patents describing the Radio RA System include U.S. Pat. Nos. 5,905,442 and 5,848,054, among others.  
         [0009]     In the existing Radio RA system, a compact radio antenna is used which comprises a planar antenna. That planar antenna, although satisfactory, has a number of disadvantages. One of the problems with the prior art antenna is that it is relatively expensive to make, requiring inductive patterns disposed on the printed circuit board determining the frequency of resonance. These planar antennas are somewhat expensive to manufacture. In addition, the antenna of the prior art device is relatively large in size, being substantially coextensive with the electrical box opening. Further, it is desirable to increase the transmission range of the antenna of the prior art device. Furthermore, the prior art device requires substantial insulation because the antenna is connected to the AC line (or “line voltage”) and is thus at the same electrical potential. Line voltage is approximately 120 V RMS  in the United States, for example, and varies throughout the countries and regions of the world. Accordingly, to provide user protection from electrical shock, the planar antenna of the prior art device requires substantial insulation members. Because the planar antenna is relatively large and because it is electrically connected to the line voltage of the dimmer, more insulation is needed when using the planar antenna, thus increasing the cost of the dimmer. The antenna of the prior art device is described in U.S. Pat. Nos. 5,982,103 and 5,736,965.  
         [0010]     It is thus desirable to provide an antenna, which offers increased performance characteristics, requires less insulation or is isolated from the AC line, and is smaller and less expensive to make.  
       SUMMARY OF THE INVENTION  
       [0011]     It is accordingly, an object of the present invention to provide an antenna for an RF communication system for controlling lamps and other electrical devices, and in which the antenna forms an integral part of a control device (e.g., a lighting control device), which can be completely installed in a conventional electrical box.  
         [0012]     It is a further object of the present invention to provide such an antenna, which is not visible, being completely contained within the lighting control device in the conventional electrical box.  
         [0013]     It is a further object of the present invention to provide an antenna as part of a lighting control device which is less expensive to make than the prior art planar antenna and which is smaller in size than the prior art planar antenna.  
         [0014]     Yet still a further object of the present invention is to provide an antenna for a lighting control device whose radiating part is isolated from the AC line, thereby reducing the amount of insulation necessary to protect the user.  
         [0015]     It is yet still a further object of the present invention to provide an antenna of compact design that provides a substantially isotropic radiation pattern, that is, a radiation pattern that is substantially the same at a defined distance from the antenna.  
         [0016]     It is yet still a further object of the present invention to provide an antenna that is easily tunable, has a broader potential frequency range and is made from readily available materials.  
         [0017]     It is yet still a further object of the present invention to provide such an antenna that has flexibility so that it is useful in different products and, in particular, useful in different control units of an RF lighting control system, for example, master unit, repeater and local lighting control unit.  
         [0018]     It is yet still a further object of the present invention to provide an antenna which is sufficiently small to fit into confined spaces, and, in particular, to serve as an integral part of a lighting control device such as a lamp dimmer installed in a standard electrical wall box.  
         [0019]     It is yet still a further object of the present invention to provide an antenna which has an increased transmission range over the prior art compact antennas used in remote control lighting control devices.  
         [0020]     The objects of the invention are achieved by a compact antenna for transmitting or receiving radio frequency signals at a specified frequency comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, and a second loop of conductive material having two ends adapted to be electrically coupled to an electronic circuit, the second loop being substantially only magnetically (or inductively) coupled to the first loop, the first and second loops having loop axes that are substantially parallel or coincidental.  
         [0021]     In a first embodiment, the first and second loops are formed by metallic layers on printed circuit boards, with the first loop being disposed on two opposite surfaces of a first printed circuit board, the first printed circuit board being disposed on a yoke of an electrical control device for mounting the electrical control device to an electrical box. The metallic surface on the outermost surface of the printed circuit board operates as the radiation element.  
         [0022]     In another embodiment, the first loop comprises a metal lance preferably stamped from the yoke of the lighting control device and having a capacitance disposed between a portion of the lance and the yoke, thereby forming an electrical current loop comprising the lance, capacitance and a portion of the yoke adjacent the lance. The lance operates as a radiation element.  
         [0023]     The objects of the invention are also achieved by a compact antenna for transmitting or receiving radio frequency signals at a specified frequency comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, and a second loop of conductive material having two ends adapted to be electrically coupled to an electronic circuit, the second loop being substantially only magnetically coupled to the first loop, the antenna comprising a part of an electrical control device, the electrical control device having a mounting yoke disposed in a plane, the first loop having a loop axis that is substantially parallel to or coincidental with the plane of the yoke.  
         [0024]     The objects of the invention are also achieved by a compact antenna for transmitting or receiving radio frequency signals at a specified frequency comprising a first printed circuit board comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency; and a second printed circuit board comprising a second loop of conductive material having two ends adapted to be electrically coupled to an electronic circuit, the second loop being substantially only magnetically coupled to said first loop of said first printed circuit board.  
         [0025]     The objects of the invention are also achieved by an electrical control device adapted to be mounted at least partly within an electrical wall box for controlling the status of a controlled electrical device, the electrical control device comprising a housing, a support yoke coupled to the housing, the support yoke having a fastening device for coupling the yoke to the electrical wall box, a controllably conductive device contained within the housing for controlling the status of the controlled electrical device, a control circuit contained in the housing, a transmitter and/or receiver contained in the housing, and an antenna adapted to receive a signal at a specified frequency from a remote control device and/or transmit a signal at a specified frequency to a remote control device, the antenna being coupled to the transmitter and/or receiver, the transmitter and/or receiver of coupling a signal from the remote control device to said control circuit for remotely controlling said controllably conductive device, and/or receiving a signal from said control circuit for providing a signal to said remote control device to indicate the status of said controlled electrical device, the antenna comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, a second loop of conductive material having two ends adapted to be electrically coupled to a control circuit, the second loop being substantially only magnetically coupled to said first loop, said first and second loops each having a loop axis, the loop axes of the first and second loops being substantially parallel or coincidental.  
         [0026]     The objects of the invention are also achieved by a remote control device adapted to be mounted at least partly within an electrical wall box, and adapted to control without a wire connection, an electrical control device connected to a controlled electrical device, the remote control device comprising a housing, a support yoke coupled to the housing, the support yoke having a fastening device for coupling the yoke to the electrical wall box, a control circuit contained in the housing, a transmitter and/or receiver contained in the housing, an antenna, at least one actuator coupled to said control circuit to provide a signal thereto to control the status of the controlled electrical device, said antenna adapted to transmit a signal at a specified frequency from the control circuit to said electrical control device, and/or receive a signal at the specified frequency from said electrical control device, the antenna being coupled to a transmitter and/or receiver, the transmitter and/or receiver of coupling said signal from said control circuit to the antenna for remotely controlling the electrical control device thereby to control the status of the controlled electrical device, and/or receiving said signal from said antenna from the electrical control device for providing a signal to said control circuit to indicate the status of said controlled electrical device, the antenna comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, a second loop of conductive material having two ends adapted to be electrically coupled to the control circuit, the second loop being substantially only magnetically coupled to said first loop, and said first and second loops each having a loop axis, the loop axes of the first and second loops being substantially parallel or coincidental.  
         [0027]     The objects of the invention are also achieved by an electrical control device adapted to be mounted at least partly within an electrical wall box for controlling the status of a controlled electrical device, the electrical control device comprising a housing, a support yoke coupled to the housing, the support yoke being disposed in a plane and having a fastening device for coupling the yoke to the electrical wall box, a controllably conductive device contained within the housing for controlling the status of the controlled electrical device, a control circuit contained in the housing, a transmitter and/or receiver contained in the housing, and an antenna adapted to receive a signal at a specified frequency from a remote control device and/or transmit a signal at a specified frequency to a remote control device, the antenna being coupled to the transmitter and/or receiver, the transmitter and/or receiver of coupling a signal from the remote control device to said control circuit for remotely controlling said controllably conductive device, and/or receiving a signal from said control circuit for providing a signal to said remote control device to indicate the status of said controlled electrical device, the antenna comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, a second loop of conductive material having two ends adapted to be electrically coupled to a control circuit, the second loop being substantially only magnetically coupled to said first loop, said first loop having a main loop axis substantially parallel to the plane of the yoke.  
         [0028]     The objects of the invention are also achieved by a remote control device adapted to be mounted at least partly within an electrical wall box, and adapted to control without a wire connection, an electrical control device connected to a controlled electrical device, the remote control device comprising a housing, a support yoke coupled to the housing, the support yoke being disposed in a plane and having a fastening device for coupling the yoke to the electrical wall box, a control circuit contained in the housing, a transmitter and/or receiver contained in the housing, an antenna, at least one actuator coupled to said control circuit to provide a signal thereto to control the status of the controlled electrical device, said antenna adapted to of transmit a signal at a specified frequency from the control circuit to said electrical control device, and/or receive a signal at the specified frequency from said electrical control device, the antenna being coupled to a transmitter and/or receiver, the transmitter and/or receiver of coupling said signal from said control circuit to the antenna for remotely controlling the electrical control device thereby to control the status of the controlled electrical device, and/or receiving said signal from said antenna from the electrical control device for providing a signal to said control circuit to indicate the status of said controlled electrical device, the antenna comprising a first loop of conductive material having at least one break in said loop and a capacitance including a capacitor bridging the break, the loop having an inductance and forming a circuit with the capacitance, the circuit comprising the loop and the capacitance being resonant at the specified frequency, a second loop of conductive material having two ends adapted to be electrically coupled to the control circuit, the second loop being substantially only magnetically coupled to said first loop, and said first loop having a main loop axis substantially parallel to the plane of the yoke.  
         [0029]     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The invention will now be described in greater detail in the following detailed description with reference to the drawings in which:  
         [0031]      FIG. 1  shows a block diagram of a radio frequency controlled lighting system making use of the antenna according to the present invention;  
         [0032]      FIG. 2  shows a simplified block diagram of a lighting control device, such as a dimmer, which is adapted to both receive control signals for controlling a lamp load as well as transmit status signals concerning the status of the lamp load;  
         [0033]      FIG. 3  shows an equivalent circuit for the antenna according to the present invention;  
         [0034]      FIG. 4  is an exploded simplified schematic perspective view of the first embodiment of the antenna according to the present invention;  
         [0035]      FIGS. 5   a  and  5   b  show a top and bottom view, respectively, of a first embodiment of the main loop printed circuit board;  
         [0036]      FIGS. 5   c  and  5   d  show a top and bottom view, respectively, of a second embodiment of the main loop printed circuit board;  
         [0037]      FIGS. 5   e  and  5   f  show a top and bottom view, respectively, of a third embodiment of the main loop printed circuit board;  
         [0038]      FIG. 6  shows an exploded view of the feed loop printed circuit board;  
         [0039]      FIG. 7  schematically shows the electrical and magnetic characteristics of the resonant loop antenna of the present invention;  
         [0040]      FIG. 8  shows a perspective view of a light dimmer according to the present invention incorporating a first embodiment of the antenna of the present invention;  
         [0041]      FIG. 9  shows a cross sectional view of a lighting control device comprising a dimmer incorporating the antenna of the present invention;  
         [0042]      FIG. 10  is an exploded perspective view of a dimmer incorporating the antenna of the present invention;  
         [0043]      FIG. 11  shows another embodiment of the antenna according to the present invention in which the main loop is formed in part by a metal part stamped from or fastened to the yoke of the electrical control device;  
         [0044]      FIG. 12  shows the feed loop of the antenna of  FIG. 11 ; and  
         [0045]      FIG. 13  shows a side view of the antenna of  FIG. 11 .  
         [0046]     Other objects features and advantages of the present invention will become apparent from the detailed description, which follows. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]     With reference now to the drawings, the antenna and control unit according to the present invention comprise components of a radio frequency controlled lighting control system. Such a system is connected into the building hardwired electrical power system  10 , shown in  FIG. 1 . Only the hot side of the AC circuit is shown in  FIG. 1 . The neutral and ground lines are not shown. With the exception of installing lighting control devices to replace the existing standard lighting control switches and dimmers, however, no change in the building wiring is necessary to implement the control functions. Accordingly, the system shown in  FIG. 1  can be used to provide remote control of a building lighting system without installing any additional wires. This is particularly useful to retrofit an existing building for remote control without expensive construction work and rewiring. However, systems of this type can also be employed in new construction to reduce the amount of wiring necessary. All control functions are accomplished by radio frequency signals transmitted between master and lighting control devices, lighting control devices and repeaters, and masters and repeaters, as appropriate.  
         [0048]     According to such a system, a master control device  20  may be installed having a plurality of controls and status indicators  22  which control various lamps assigned to the various control actuators. The assignment of the particular lamps to particular control buttons can be in accordance with the previously known Lutron Radio RA system. That system is described, for example, in U.S. Pat. Nos. 5,905,442 and 5,848,054, among others, the entire disclosures of which are incorporated by reference herein. The master device  20  includes an internal antenna, which is hidden from view (or an external antenna) and receives and transmits radio frequency signals for control and status functions. The master device  20  plugs into a wall outlet  25  for power via an AC transformer  26 . If desired, additional master devices  20  can be provided. A wall mounted master unit or units  30  can also be provided. The master unit  30  is identified as a wall-mount master because it is installed into an existing electrical wall box. The wall mount master  30  may also include an internal antenna according to the inventions, which is hidden from view. Any number of master units, either of the table top type  20  or all wall-mount type  30  can be provided in the system.  
         [0049]     According to the system described, a repeater (or repeaters)  40  may also be provided to ensure that every component of the system will receive the RF communication signal for control purposes. The repeater  40  includes an external antenna  24  (or a hidden antenna) for transmitting and receiving radio frequency signals. The repeater may be powered by a transformer  26 A plugged into wall outlet  25 . The repeater is described in the above-identified patents. Note that repeater  40  and master device  20  could be battery powered rather than via AC transformer  26 .  
         [0050]     At least one lighting control device  50  is provided which includes an antenna according to the present invention. The lighting control device  50  is capable of manual actuation via a manual control button  52 , but which is also capable of receiving radio frequency signals from the master units  20 ,  30  or repeater  40  to control the status of a lamp  54 . In addition, the lighting control device  50  is preferably capable of transmitting radio frequency signals to the repeater  40  and master units  20  and  30  to inform the master units of the status of the affected lamp or lamps  54 . The lighting control device  50  may comprise a dimmer, for example, and may include a plurality of status indicating devices, for example, light emitting diodes (LEDs) and/or optical fibers  56 , which indicate the intensity and setting of the lamp  54  to the user. The indicators  56  may be direct view LEDs or fiber optic pipes, which receive light energy from suitable illumination devices such as light emitting diodes. In addition, the lighting control device  50  includes a means  58  for setting the intensity level, for example, such means  58  may comprise an up/down rocker switch. Furthermore, an on/off switch  59  may be provided to disable the operation of the lamp. The on/off switch  59  may comprise an air gap switch that completely isolates the lamp from the dimmer circuit, for example, when performing lamp maintenance. A plurality of lighting control devices  50  controlling respective lamps  54  can be provided according to the system described. While dimmer  50  and master  30  are described here as having the antenna according to the present invention, the master unit  20  and repeater  40  could also have such an antenna.  
         [0051]      FIG. 2  shows a simplified block diagram of the lighting control device  50 , which is capable of both receiving and transmitting RF signals. The HOT terminal of the lighting control device  50  is connected to an electrical power system  10  and the DIMMED HOT terminal is connected to the lamp load  54 . The neutral line connected to the lamp load  54  need not be connected to the lighting control device  50 . In this way, the lighting control device  50  can replace a simple two-wire on/off switch or dimmer.  
         [0052]     This lighting control device  50  has a user input means  102 , which may comprise suitable switches or controls for providing on/off and dimming functions. A triac  106  (or other suitable power conducting semiconductor) controls the amount of power delivered to the lamp load  54  as determined by a control circuit  108 . The antenna of the present invention  300  is connected to a transceiver  110  via a DC (direct current) blocking capacitor  114  to eliminate DC current in the antenna. The transceiver  110  is also coupled to an encoder/decoder  112 , which is coupled to the control circuit  108 . The transceiver  110  is capable of both transmitting RF signals to the antenna  300  for transmission and for receiving RF signals for controlling the control circuit  108 . A power supply  116  provides power to the control and other circuits of the dimmer  50 . For example, the power supply  116  may be a “cat-ear” power supply, which obtains power only during those portions of a cycle when the triac  106  is off, thereby preventing voltage drops to the lamp load  54 . The user input  102 , triac  106 , control circuit  108 , transceiver  110 , encoder/decoder  112 , and power supply  116  are all mounted on a dimmer circuit printed circuit board (PCB)  118 .  FIG. 3  shows an equivalent circuit of the antenna  300  according to the present invention. The antenna  300  is comprised of two parts: a main loop  210  and a feed loop  250 . The main loop  210  is the primary radiating element of the antenna  300  and includes an inductance L and capacitance C in series. When energized, the main loop  210  resonates at a frequency determined by the values. of L and C and enables the transmitting and receiving of RF signals via a radiation resistance, R r , which is a representation of the energy delivered to radiation. The losses in the main loop  210  are represented by a loss resistance, R l . The main loop  210  is primarily magnetically coupled to the feed loop  250 . This coupling is shown schematically in  FIG. 3  by an ideal transformer T. The feed loop  250  includes a magnetizing inductance L m , a leakage inductance L l , and two ends  357  that connect to the dimmer circuit PCB  118  via capacitor  114 . The feed loop  250  allows for the conduction of signals between the dimmer circuit PCB  118  and the main loop  210 . In this way, the antenna  300  is adapted to receive signals via the main loop  210 , with those radio frequency signals being electromagnetically coupled to the feed loop  250  for input to the RF circuit transceiver  110 . Conversely, the feed loop  250  receives signals to be transmitted from the transceiver  110 , electromagnetically couples these signals to the main loop  210  for transmission of RF signals to a master or repeater device.  
         [0053]      FIG. 4  shows a perspective simplified schematic exploded view of this embodiment of the antenna  300  of the present invention. According to the present invention, the antenna  300  comprises a resonant loop antenna comprising a main loop printed circuit board (PCB)  310 , which preferably comprises a printed circuit board, preferably ⅛ inch thickness FR4 printed circuit substrate, on which is deposited a conductive material  314 , e.g., copper, aluminum or steel, on both upper and lower sides. The conductive material  314  on the upper and lower sides are connected by vias  312  provided to form a loop for current flow between the upper and lower sides of the main loop PCB. The main loop PCB  310  has an inherent inductance that supplies the inductance L as shown in  FIG. 3 . The main loop PCB  310  also includes a slot  360 , sized to allow the feed loop printed circuit board (PCB)  350  to fit within the slot in a perpendicular orientation to the main loop PCB. The feed loop PCB  350  may comprise a 62-mil thickness FR4 printed circuit board having two ends  357  adapted for connection to the dimmer circuit PCB  118  of the lighting control device  50 .  
         [0054]     A top view and a bottom view of the main loop PCB  310  are shown in  FIGS. 5   a  and  5   b , respectively. One of the layers of conductive material  314 , e.g., on the bottom side of the main loop PCB  310 , is provided with a break or slot  316 . Across the slot, suitable surface mount capacitors  315  may be disposed to provide, along with an inherent capacitance of the main loop PCB, the capacitance C as shown in  FIG. 3 . The capacitors may comprise, for example, surface mount capacitors, which can be trimmed (using a trimmable capacitor) to adjust the resonant frequency of the main loop. The capacitors thereby form, with the printed circuit, an LC circuit. The current in the LC circuit is at a maximum magnitude when the RF signal being transmitted or received is at the resonant frequency determined by the inductance L and capacitance C of the main loop PCB  310 .  
         [0055]     Apertures  340  in the main loop PCB  310  allow for attachment of the main loop PCB with the dimmer  50  by a heat stake, which is an insulating fastener that does not change the magnetic characteristics of the main loop PCB. The heat stake is made from a thermoplastic material and comprises two straight posts that fit through apertures  340  in the main loop PCB  310 . The ends of the posts are formed by the use a horn, which is heated in order to melt the thermoplastic material. After the heat staking process, the ends of the posts have a diameter greater than the diameter of the apertures  340 , thus holding the main loop PCB  310  in place. Alternatively, other means of forming the ends of the posts may be used, such as ultrasonic staking, in which the ends are heated and formed by vibration of the horn. This design allows for attachment of the main loop PCB  310  at areas of minimal current density. It has been determined that the areas of maximum current density are at the edges  342  of the main loop PCB  310  so that in this embodiment, there is less interference with the current flow in the main loop. However, other means such as snap connections at the edges of the main loop PCB  310 , may be used.  
         [0056]     The top side of the main loop PCB  310  is provided with interdigitated fingers  320  that provide means for trimming the inherent capacitance of the LC circuit forming the resonant main loop. The outer fingers  322  and the inner fingers  334  are separated from each other by a break  326 . The inner fingers  324  are coupled to the conductive material  314  on the bottom side of the main loop PCB  310  by via  328 . The fingers are trimmed by cutting away the copper using a laser or other means of cutting. Trimming the inner fingers  324  produces a greater change in the capacitance of the main loop PCB  310  than trimming the outer fingers  322 .  
         [0057]      FIGS. 5   c  and  5   d  show the top view and bottom view, respectively, of a second possible embodiment of the main loop PCB  310 A. A different configuration of interdigitated fingers  320 B is shown on  FIG. 5   c . The interdigitated fingers  320 A have a greater number of outer fingers  322 A and inner fingers  324 A separated by break  326 A. Via  328 A connects the inner fingers  324 A with the layer of conductive material  314 A on the bottom side of the main loop PCB  310 A. Once again, the fingers are trimmed by cutting away the copper using a laser and trimming the inner fingers  324 A produces a greater change in the capacitance of the main loop PCB  310 A than trimming the outer fingers  322 A.  
         [0058]      FIG. 5   c  shows the main loop PCB  310 A with at least one laser cut slot  318  in the conductive material  314 A. The laser cut slots  318  adjust the inductance L of the main loop PCB  31  OA since the inductance of a conductor is dependent on the length, width, and thickness of the conductor. In this way, the resonant frequency of the main loop PCB  310 A can be adjusted by trimming away conductive material  314 A of the main loop PCB by providing the laser cut slots  318  of varying thicknesses and lengths. Even though trimming away the conductive material  314 A provides a means for changing the inductance L of the main loop PCB  310 A, trimming the conductive material also increases the loss and decreases the efficiency of the main loop PCB.  
         [0059]      FIGS. 5   e  and  5   f  show the top view and bottom view, respectively, of a third possible embodiment of the main loop PCB  310 B, showing further means for changing the inductance L and capacitance C of the main loop PCB  310 B. Capacitive fingers  320 B provide means for trimming the capacitance of the main loop PCB  310 B. Inner fingers  324 B are separated from the conductive material  314 B on the top side of the main loop PCB  310 B by breaks  326 B and are connected to the conductive material  314 B on the bottom side of the main loop PCB  310 B by vias  328 B. The inner fingers  324 B are trimmed by cutting away the copper using a laser.  
         [0060]     On the bottom side of main loop PCB  310 B, seven surface mount capacitors  315 B are shown, each connected to a separate via  312 B as shown in  FIG. 5   f . On the top side, each of the five inner vias  312 B are connected to the conductive material  314 B by traces  330 . By cutting one or more of the traces  330  with a laser, the capacitance of the main loop PCB  310 B is changed by simply removing the capacitor  315 A attached to the trace  330  from the circuit.  
         [0061]     Traces  332  on the top side of main loop PCB  310 B provide a means for trimming the inductance of the main loop PCB. When these traces are cut, the inductance L of the main loop PCB  310 B changes since the inductance of a conductor is dependent on the length, width, and thickness of the conductor.  
         [0062]      FIG. 6  shows an exploded view of the feed loop printed circuit board  350  also shown in  FIG. 4 . Three layers of insulation  352 , made from FR-4 printed circuit board substrate, are located between four layers of a suitable conductive material (e.g., copper, aluminum, steel). The two inner layers of conductive material include feed loop traces  355 , which are coupled in parallel and are insulated from external contact with the main loop PCB  310  and yoke  518  by the outer insulating layers  352 . The feed loop traces  355  are connected to the two ends  357  through vias  362  and are surrounded by inner shielding  354  and outer shielding  353 , which both may be copper, aluminum or steel or any suitable metal and acts to shield the circuitry of the lighting control device from RF interference. The outer shielding  353  and inner shielding  354  are connected by vias  364 .  
         [0063]      FIG. 7  schematically shows the electrical and magnetic characteristics of the resonant loop antenna of the present invention. The main loop PCB  310  has a main loop axis, which is parallel to the Z-axis. As shown, RF signals received by the main loop PCB  310  induce a current flow I through the upper and lower surfaces of the main loop PCB. Current flows through the vias  312  at each end and is at a maximum magnitude when the RF signal being transmitted or received is at the resonant frequency determined by the inductance L and capacitance C of the main loop  210 . The current flow induces a magnetic field Φ as shown. The magnetic lines of flux intersect the feed loop  250 , causing a current to be induced in the feed loop for input to the receiver of the RF circuit. When transmitting, RF signals in the feed loop PCB  350  are electromagnetically coupled to the main loop PCB  310  by the magnetic field Φ, establishing a current flow in the main PCB  310  at the resonant frequency for transmission as radio frequency signals.  
         [0064]     The antenna  300  provides a substantially isotropic radiation pattern, meaning that the antenna radiates relatively uniformly in all directions over a sphere centered on the antenna. There are no locations on the sphere in any direction where the radiated power equals zero. This means that the antenna  300  can be mounted in any fashion, i.e. horizontally or vertically, and still perform suitably.  
         [0065]      FIG. 8  is a perspective view of a dimmer lighting control device  50  incorporating the antenna  300  according to the present invention. The faceplate, as well as the actuating switch mechanisms  52  and  58  for controlling the on/off operation and lighting intensity of the lamp, is not shown in  FIG. 8 . These mechanisms would be disposed on top of the dimmer assembly shown in  FIG. 8 . These mechanisms have purposely not been shown in  FIG. 8  so as to reveal the structure of the antenna according to the present invention. However,  FIG. 10  shows details of the on/off and dimming actuating mechanisms.  
         [0066]     With reference to  FIG. 8 , a perspective view of a light dimmer  50  incorporating the antenna of the present invention is shown. The light dimmer  50  includes a housing including a back cover cap  500 . The housing houses the electronic circuitry of the light dimmer including power/dimming circuitry, control electronics and RF circuitry. A screw terminal  554  is included on the back cover  500  for connection of AC hot from the electrical power system  10  to the dimmer  50 . Another screw terminal  550  allows for connection of dimmed hot to the load  54 . A screw terminal  552  connects to neutral (if required). A fourth screw terminal  556  (shown in  FIG. 6 ) allows for connection of an accessory control link.  
         [0067]     The dimmer includes a yoke  518  which is typically made of metal, e.g., steel or aluminum, and is adapted to enable the light dimmer to be secured in an electrical wall box in conventional fashion using screws through holes  522 . The yoke  518  is preferably made of metal to provide a heat sink for the power dissipating components of the dimmer. The yoke  518  includes a number of apertures therethrough to be described in greater detail with reference to  FIG. 10 , which allow actuation of the dimmer controls, i.e., the on/off function as well as setting the dimming levels. For example, apertures  538 A and  538 B allow entry of projections from a dimmer rocker mechanism to actuate a dimmer setting switch disposed in the interior of the dimmer  50 . In addition, apertures  540  are provided to allow the illumination from light emitting diodes (LEDs), which display the intensity level of the lamp attached to the control, to shine through the yoke  518 . The metal yoke  518  is preferably coupled to earth ground through a wire that is connected to ground connection means  516 .  
         [0068]     In the center of the yoke  518 , the antenna of the invention  300 , is provided. According to the embodiment shown in  FIG. 8 , the antenna of the invention comprises the main loop PCB  310  and the feed loop PCB  350  disposed substantially perpendicularly to the main loop PCB  310  and in a slot  360  of the main loop PCB. The main loop axis of the main loop PCB  310  is parallel to the plane of the yoke  518 . Since the metal yoke  518  of the dimmer  50  is preferably grounded, the main loop  310  must be mounted on the outer surface of the yoke  518 . The feed loop printed circuit board is isolated from the main loop and coupled to it substantially only magnetically. The main loop printed circuit board  310  may be held to the yoke by a heat stake having posts  528 , which attach the main loop to the yoke at areas of minimal current density as explained above. There is an aperture in the yoke  518  at the location where the capacitors  315  are mounted on the bottom side of the main loop PCB  310  when the main loop PCB is attached to the yoke to prevent contact with the capacitors and the yoke.  
         [0069]      FIG. 9  shows a side cross sectional view of the dimmer  50 , without the faceplate, dimmer and on/off controls. The main loop PCB  310  is attached to the yoke  518  by heat stake  526 , which is an insulating fastener that does not change the magnetic characteristics of the main loop PCB. As explained above, the heat stake  526  is made from a thermoplastic material and comprises two straight posts  528  that fit through apertures  340  in the main loop PCB  310 . The ends of the posts  528  are formed by the use a horn, which is heated in order to melt the thermoplastic material. After the heat staking process, the ends of the posts  528  have a diameter greater than the diameter of the apertures  340 , thus holding the main loop PCB  310  in place. The ends  357  of feed loop PCB  350  are connected to slots  504  on the dimmer circuit PCB  502 . The feed loop PCB  350  is mounted perpendicular to the main loop PCB  310  and in the slot  360  in the main loop PCB. The feed loop PCB  350  is electrically coupled to the RF portion of the dimmer circuit board  502  via the ends  357 . Note that when feed loop PCB  350  is installed in the dimmer  50 , the outer shielding material  353  is below the plane of the yoke  518 .  
         [0070]      FIG. 10  shows details of the construction of the lighting control device  50  incorporating the antenna according to the present invention.  FIG. 10  is an exploded view of the lighting control device  50  of  FIGS. 8 and 9 . The lighting control device  50  includes an insulating back cover cap  500  having screw terminals  550 ,  552 ,  554 ,  556  to which the electrical wires can be provided for Dimmed Hot, Neutral, Hot, and accessory control, respectively. Into the back cover cap  500 , a dimmer printed circuit board  502  is provided coupled to the antenna  300  already described. The feed loop PCB  350  connects to slots  504  in the dimmer PCB  502 . The purpose of the dimmer PCB  502  is to receive radio frequency signals from the antenna  300  for controlling the operation of the lamp as well as for feeding radio frequency signals to the antenna  300  for transmission back to the master devices. The dimmer PCB  502  also includes a suitable power supply  116  and a microprocessor control circuit  108  that is controlled by signals received from the antenna  300  and which transmits signals to the antenna  300  concerning the status of the controlled lamp. The dimmer PCB  502  also includes a plurality of light emitting diodes (LEDs)  506 , which indicate the status of the affected lamp. A light pipe assembly  531  is provided above yoke  518  and couples the light from each of the light emitting diodes  506  externally of the device to display the dimming status of the controlled lamp.  
         [0071]     Coupled to the back cover cap  500  is a back cover ring  510  also made of an insulating material. The intensity of the lamp controlled by the dimmer printed circuit board  502  is controlled by a semiconductor power device  514 , which may comprise a triac. Power semiconductor device  514  is held in place by post  512  of back cover ring  510 , such that the power semiconductor device  514  is in contact with the metal yoke  518  to dissipate heat. The yoke  518  thus comprises a heat sink and also functions as the means by which the lighting control device  50  is mounted into an electrical wall box. Accordingly, yoke  518  includes two screw holes  522  receiving mounting screws for mounting the yoke and accordingly, the device  50  into the electrical wall box in conventional fashion. The main loop PCB  310  is fastened to the yoke  518  near the center of the yoke by heat stake  526  having posts  528 . The feed loop printed circuit board  350  of the antenna  300  is coupled to the dimmer PCB  502 .  
         [0072]     Disposed above the yoke  518  is an actuating button  52  operating through the intermediary of a hinge bar  532  to control a switch  534  on dimmer PCB  502 . The switch  534  is operated by the hinge bar  532  and provides signals to the control circuit  108 , which controls the operation of the power semiconductor device  514  to control the on/off status of the dimmer  50 . In addition, a rocker arm control  538  is provided having operating surfaces  58  for increasing and decreasing the intensity level of the connected lamp by contacting switches  536  on the dimmer PCB  502 . An air gap actuator  59  operates an air gap switch to provide a positive air gap system-off for system maintenance. Bezel  530  is provided as an outer covering for aesthetic purposes and may be suitably colored. Preferably bezel  530  and members  52 ,  59  and  538  are each factory installed in one of selected colors so that an appropriate aesthetic appearance can be obtained. These respective components are interchangeable so that different colors or color combinations can be provided.  
         [0073]     In contrast to the prior art antenna shown in U.S. Pat. Nos. 5,982,103 and 5,736,965, the entire disclosures of which are incorporated by reference herein, because the main loop printed circuit board  310  is electrically isolated from the feed loop printed circuit board, the amount of insulation necessary between the user actuatable and contactable surfaces  52 ,  58 ,  59 ,  530  and the face plate of the lighting control device and the AC-connected portions of the lighting control device is reduced. In particular, the main loop printed circuit board  310  is completely isolated from the feed loop printed circuit board  350 . The main loop printed circuit board  310  is preferably electrically connected to the yoke  518 , but it may be insulated from the yoke  518  with a small insulating member between the printed circuit board and the yoke.  
         [0074]     The feed loop printed circuit board  350  is electrically connected to the power lines  10  and thus may be at line voltage potential. However, because of the isolation provided by the magnetic coupling between the feed and main loops, the main loop printed circuit board  310  is not at line voltage potential. If the main loop is connected to the yoke  518 , it will thus be connected to earth ground via the ground network of the electrical system  10 .  
         [0075]     In addition to the above benefit, the antenna of the present invention is much smaller than the planar antenna shown in the prior art patents, occupying only a small portion at the center of the yoke  518 .  
         [0076]      FIG. 11  shows another embodiment of the antenna according to the present invention for use in an electrical control device.  FIG. 11  shows the yoke  382  of the electrical control device. The antenna  380  comprises a lance  384 , which is stamped out of the metal plate of the yoke  382 . Alternatively, the lance  384  could be fastened with screws, rivets or other fasteners or fastening means (e.g. welding) to the yoke  382 . The lance  384  is disposed a predefined distance above the plane of the yoke  382  and is separated from the yoke  382  by this distance. At the end  386  of the lance  384 , the lance tip  386  is separated from the yoke  382  by a dielectric member  388 , which acts as a capacitance between the end  386  of lance  384  and the yoke  382 . Accordingly, the lance  384  acts as a radiating and/or receiving member of the antenna  380 . Therefore, when acting as a receiver, currents are induced in the loop comprising the lance  384 , the dielectric member  388  and the portions of the yoke  382  below the lance  384  and adjacent it. Accordingly, a current loop is formed having a main loop axis substantially parallel to the plane of the yoke  382 .  
         [0077]      FIG. 12  shows one embodiment of a feed loop  390 , which can be used with the lance  384 . It is disposed through an opening  392  formed below the lance  384 . In particular, it would be disposed through the opening  392  that is created when the lance  384  is stamped out of the yoke  382 . Alternatively, if the lance is secured to the yoke by fasteners or welded or otherwise fastened to the yoke, an opening  392  is formed below the lance  384  sized to receive the feed loop  390 . The feed loop  390  can also be disposed on a printed circuit board or on some other substrate and may have insulation thereon as in the previously described embodiments to electrically isolate it from the yoke and the main loop. The feed loop  390  has two ends  396  for connection to the RF control circuitry.  
         [0078]      FIG. 13  provides a side view of the antenna  380  showing how the feed loop  390  fits into the opening  392  in the yoke  382  under the lance  384 .  
         [0079]     The dielectric member  388  may be made from suitable material. One suitable material is Rodgers  4010  or  3010  material and it can be laser trimmed. A suitable clamping means may be provided to clamp the lance end  386  to the dielectric member  388  to prevent inadvertent changes in the capacitance.  
         [0080]     Alternatively, the lance  384  can be coupled to the yoke at both ends by a dielectric member  388 , effectively distributing the capacitance between the two ends of the lance  384 .  
         [0081]     Any other suitable dielectric material can be chosen for the dielectric member  388 . It is preferable that a low loss material be used. Losses in the resonating capacitor will directly detract from the efficiency of the loop.  
         [0082]     Another source of possible losses in the loop/capacitor combination is in the dissimilar metals forming the yoke-to-capacitor junctions. If the yoke is formed of aluminum, the aluminum should be abraded prior to making the pressure contact and means to ensure continued pressure and additional oxidation prevention should be used. The PCB forming the capacitor should preferably be tinned, since a tin/lead aluminum junction has a lower potential for corrosion than an aluminum-copper junction. Plating selected areas (or “spot plating”) of the yoke may also be possible.  
         [0083]     In an embodiment of the antenna  380 , the top of the lance  384  of the main loop is 0.125 inch above the surface of the yoke. The lance is 0.045 inch thick and 0.120 inch wide. The loop is 2.18 inches long. The loop can be made longer. The efficiency improves as the loop is made longer and thus the enclosed area larger.  
         [0084]     The efficiency of the antenna  380  is directly related to the area enclosed by the loop. The height of the lance  384  above the yoke  382  is thus the most sensitive parameter for efficiency. This height is directly limited by the thickness of the plastic face of the dimmer. To provide maximum benefit, the antenna  380  should extend as far as possible towards the faceplate of the lighting control device.  
         [0085]     Preferably, the feed loop  390  shown in  FIG. 12  is inserted into the slot  392  in the yoke  382  below the lance  384 . The feed loop  390  could be encapsulated in plastic to provide the voltage isolation required.  
         [0086]     The feed loop  390  may be made from flat metal stock, for example, 0.015 inch brass. The top of the loop is preferably folded over which enables close magnetic coupling with the main loop, limited by the thickness of the insulation between them as required by the dielectric breakdown requirements. This is shown in  FIG. 12  by the fold-over  394 . The plastic housing of the feed loop may anchor the main loop lance  384  setting the antenna height and providing protection from damage.  
         [0087]     Since the coupling between the main loop and the feed loop is substantially via the magnetic field, the dielectric constant of the plastic material encapsulating the feed loop is relatively insignificant.  
         [0088]     There has thus been described a resonant loop antenna as well as an electrical control device incorporating a loop antenna wherein the loop antenna has a main loop radiating receiving part which is primarily magnetically coupled to a feed loop.  
         [0089]     Further, the radiating and receiving main loop is isolated from the feed loop because of the inductive coupling and thus does not require any additional isolation means to prevent the danger of electrical shock. A desired feature of a dimmer is the ability to replace the entire user interface assembly (faceplate, button, bezel, rocker arm, etc.) with a user interface having a different color in the field, the dimmer cannot be potentially harmful when the user interface is removed and the yoke and antenna are exposed to the user. This means that there must be suitable electrical isolation between the high voltage circuitry on the dimmer PCB  502  and any surface that the user can touch to prevent electrical shock.  
         [0090]     Furthermore, the antenna is easily tunable over a wide range because it can be tuned by adjusting only one element, either the inductance or capacitance while maintaining the characteristic impedance at a given value. Adjusting the capacitance is generally preferable since adjusting the inductance may increase the losses in the main loop.  
         [0091]     Furthermore, the primary and leakage inductances are weakly coupled. The antenna comprises a series resonant antenna and can be tuned separately from the drive circuit. Furthermore, the antenna is field changeable so that the frequency of operation can be changed easily. The feed loop can be shielded to minimize noise and it can be surrounded by insulating materials to obtain further isolation. Furthermore, the antenna provides advantages over the prior art compact antennas in electrical control devices because the transmission range is extended, and is more easily tunable.  
         [0092]     Furthermore, the antenna of the invention is less expensive to manufacture than the antennas of the prior art.  
         [0093]     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention should be limited not by the specific disclosure herein, but only by the appended claims.