Patent Application
20090102677
The invention relates to a device for integrating a compact RF antenna held for transmitting and receiving radio frequency signals, into a wireless lighting control system installed in a standard electrical wall box. Other antennas may generally relate to this field. For example, the following U.S. patents generally relate to the field: U.S. Pat. No. 4,138,684 to Kerr; U.S. Pat. No. 4,939,702 to Urbish et al; U.S. Pat. No. 5,079,559 to Umetsu et al; U.S. Pat. No. 5,400,041 to Strickland; U.S. Pat. No. 5,982,103 to Mosebrook et al, wherein the disclosures of all of these patents are hereby incorporated herein by reference.
A good or effective antenna can create an electromagnetic (EM) field in space. This antenna will have a radiation resistance that is much larger than the loss resistance. In that way, radio frequency (RF) power is dissipated into space as opposed to dissipated in the antenna materials.
In addition, an effective antenna presents suitable impedance to the RF interface circuitry which can usually be at 50 ohms resistance with nearly 0 ohms reactive. This antenna impedance is measured using a network analyzer.
Furthermore, an effective antenna prevents standing waves on the host device by minimizing common mode currents. With the case of a wall switch, the need for low common mode currents is increased so that connections to the device do not cause excessive performance variation.
In most cases, the connection between RF circuits consists of an unbalanced transmission line, such as for example a coaxial cable, or a microstrip transmission line. Unbalanced transmission lines ideally carry differential mode currents only. However because an antenna inherently interacts with the environment, it can excite currents on the ground if not interfaced properly. This can lead to common mode currents.
Proper interfacing will match the antenna to the transmission line. A balanced antenna like a dipole will often include a Balanced to Unbalanced transformer (a BALUN). Other antennas like an “F” antenna naturally interfaces with unbalanced lines.
Common mode currents result in that an unintended voltage is established somewhere besides the antenna. One effect is that the performance can be sacrificed because power can be lost as the voltage induced radio waves are radiated inside of the appliance. Alternatively, destructive interference is established resulting in a highly irregular radiation pattern.
The design of the present invention is in contrast to previous designs which might relate to a traditional F antenna. A traditional “F” antenna naturally interfaces to the unbalanced transmission line by establishing a ground at the surface of the device. There is radiation resistance in the interval between the feed point and the open ended transmission line and the interval between the feed point to the ground connection that establishes the input impedance.
In contrast, the present invention overcomes some of the limitations of the prior art by providing for example, a modified “F” antenna that results in an antenna positioned on a different plane from an antenna feed point.
The present invention relates to a wireless lighting control system which uses a compact but concealed antenna connected to the lighting control system such as, for example a light dimming system for turning on and off a light or dimming a light to a certain level in response to an external RF signal. In the construction of the antenna of the system, the antenna selected, which resides behind the switch plate, has a length that is less than a quarter of the transmitted or received wavelength. The antenna comprises a single wire antenna that is suitably loaded by the use of stripline-like components to produce a tuned, sensitive antenna for receiving and transmitting RF signals within the local area of the wall switch.
For example the invention can relate to a remote control electrical device such as a wireless lighting system which can communicate with a remote control device. In this case, the wireless lighting system is adapted to fit into a housing which fits into a wall mounting. The lighting system comprises a control circuit and a transmitter disposed in the housing. There is also a receiver disposed in the housing wherein the transmitter and the receiver are in communication with the control circuit. There is also a support plate in the form of a strap having an inside face and an outside face. The strap is coupled to the housing. There is also an antenna, wherein the antenna is adapted to receive signals from the remote control device and transmit signals to the remote control device. This antenna is in communication with the transmitter, and the receiver. In addition, the antenna can be coupled to the outside face of the support plate.
Many of these electrical components are housed on at least one printed circuit board, wherein the control circuit as well as the transmitter and the receiver are disposed on the printed circuit board.
For example, the transmitter and the receiver can be in the form of a transceiver mounted on the printed circuit board. However, this antenna is not mounted on the circuit board but capacitively coupled to the printed circuit board.
Thus, there can be at least two isolating capacitors disposed on the printed circuit board and coupled in series between the antenna and the transceiver.
There can also be an antenna feed point, in the form of a strip line that is capacitively coupled to antenna and disposed on the printed circuit board.
One advantage of the invention is that the strap can extend outside of the housing. The strap is in the form of a plate which can be made from aluminum. Coupled to the strap is at least one antenna coupler. This antenna coupler is comprised of a dielectric material which effectively isolates the antenna from the strap. This antenna coupler includes a channel for receiving the antenna and at least one prong for selectively securing the antenna to the support plate.
In one example embodiment, the antenna can comprise a flexible wire that can be any shape such as in an L shape and disposed inside a thin insulation, and mounted on the strap plate so as to be concealed by the cover plate of the wall switch. The antenna is “tuned” with respect to the ground plane of the printed circuit board of the lighting control, and the metal surrounding the antenna. The antenna is capacitively coupled to the circuit board of the lighting control so as to prevent any electrical hazard with respect to the line voltage supplied to the control circuit. The compact antenna design provides flexibility with regard to changing the color of the frame or wall plate. In addition, because of the presence of the antenna feed point, the antenna is also not disturbed by any hand or body effect located in close proximity to the switch so that there is no detuning of the circuit due to any hand or body effect.
Other features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings.
In the drawings, wherein similar reference characters denote similar elements throughout the several views:
Referring to
Air gap switch 12, which is connected to the 110 volt AC line, is a mechanical switch or relay that will disconnect the power to the control circuitry when the two contacts of gap switch 12 are physically separated, such as when the switch is exposed or opened up for inspection.
Main controller 10 controls the functions of the load. In particular, it can be used to control the amount of power using the switching and dimming circuit 13 directed to the load 9 (for example a dimmer switch, and on/off switch etc). Main controller 10 can include a processor and works in communication with the communication controller and the memory chip.
Secondary controller or RF Transceiver 14 is used to control the wireless communication between antenna 20 and the other logic components such as main controller 10 and memory chip 15.
Memory chip 15 is an EEPROM memory chip that can be in communication with secondary controller 14. This EEPROM is encoded with, and can be used to store the following characteristics: last load status, light level, minimum and maximum settings or other known settings. In this case, the EEPROM also offers power down storage and retrieval of events status during power up. A power supply 11 is shown coupled between switch 12 and the controller and switching circuits. The above circuits would typically be contained on a printed circuit board mounted within the housing of the unit.
Referring to
Saw filter 26 is similar to a band pass filter and is tuned to a particular signal to pass on signals of a selected band width.
Referring to
Printed circuit board (PCB) 60 includes a copper plated or conductive ground plane 29 which is an electrically conductive surface that serves as a near-field reflection point for an antenna, or as a reference ground in a circuit. This ground plane helps reduce noise and helps to ensure that all integrated circuits within the system compare different signal voltages to the same potential. This ground plane 29 is shown by the cross hatched area. Another printed circuit board or PCB 50 (See
Antenna 20 is designed for the reception and transmission of control signals at for example, 908 MHz frequency. The antenna is fed single ended and can have an impedance of any other number other than 50 ohms at resonance frequency. Matching to a 50 Ohm circuit includes correctly positioning the antenna feed point which serves as a tap point on a transmission line transformer. It was found that an antenna of 1.67 inches long, which is smaller than the ¼ wavelength of 3.24 inches for that frequency of 908 MHz worked very well. The impedance of the RF transceiver and the SAW filter is approximately 50 ohm at the transmitting frequency.
Ultimately, the benefit of this design is that the radiating part of the transmission line or antenna is above the outer surface of the device. The antenna tap and the feed point 17 are inside of the housing or device. This method reduces the required outer surface area and allows the “loop” between the ground and the feed point to be manufactured on a standard printed circuit board which also simplifies the assembly and reduces cost.
There are various ways to match the antenna impedance. The first method is to use a matching network between the SAW filter and antenna. The matching network can either be a “T” or a “π” structure, or part of that structure. A second method for matching the impedance is the use of antenna feed point 17 wherein the shape of the feed point, the trace width of the feed point, the spacing between the feed point and ground plane and antenna length adjusted during the tuning process will achieve the desirable antenna impedance (50 ohm in our case) and return loss (better than −25 dB at 908 MHz).
The hand/body effect can cause a detuning of an antenna impedance characteristic when there is a human touch to the area close to the antenna.
The design of the antenna system of this invention however avoids the hand and body effect on reception/transmission by its unique design of the antenna feed point. The antenna feed point provides a fixed impedance that is insensitive to the environment, i.e. relatively insensitive to the material of wall box in which the product is installed and insensitive to the presence of other environmental factors such as persons or other metal or plastic objects in close proximity to the antenna.
Referring to
Referring to
For example, in this embodiment there is shown a housing 40 which is designed to fit into a wall box, and receive a circuit board 50, a first circuit board 60 having an air gap switch 12, a second board 66 is spaced apart from first circuit board 60 by spacing columns 64. Both circuit boards can be housed inside of housing 40. There is strap 35 which can be coupled to housing 40 via screws 80 and positioned to extend outside of housing 40. As shown in this view, coupled to strap 35 is antenna holder 30 which holds antenna 20 in a position essentially outside of housing 40. Because strap 35 functions as a heat sink for circuit boards 60 and 50, the position of strap 35 outside of housing 40 allows for greater heat dissipation outside of housing 40 creating a greater tolerance for electrical power to pass through circuit boards 60 and 50.
A bezel 70 is coupled to the face of strap 35 which can be used to allow a switch plate 75 to be coupled thereto and house a switch 72 beneath switch plate 75.
Thus, with this design, a strap can extend outside of a housing providing a greater heat dissipation from the electronic components inside of the housing while allowing the antenna to be coupled in front of the strap creating greater access to the antenna and improved reception. In addition, because the antenna is capacitively coupled to the electronic components, a user touching this antenna on the strap would not be subject to AC current running through this antenna. Thus this creates a safer, improved wireless system.
Accordingly, while a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.
