GB2543934A

GB2543934A - Fob with increased power level from hand-antenna coupling

Info

Publication number: GB2543934A
Application number: GB1616037.6A
Authority: GB
Inventors: Wisnewski Mark; Arthur Winkel Tye; Frederick Locke John; Banasky Lawrence; Joseph Hermann Thomas
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-09-23
Filing date: 2016-09-21
Publication date: 2017-05-03
Also published as: GB201616037D0; MX2016012300A; RU2016137645A; DE102016116904A1

Abstract

Disclosed is a key fob 14 that has a power amplifier with an output having an output impedance. The key fob also has a radio frequency antenna connected to the power amplifier output that represents a first load impedance to the power amplifier output in a space free of radio frequency transmission interference, and a second load impedance to the power amplifier output when a hand of a user is in capacitive contact with the antenna. Wherein the difference between the second load impedance and the output impedance of the power amplifier is less than the difference between the first load impedance and the output impedance. The key fob may also have an electrical load network connected between the power amplifier output and reference potential, eg ground, wherein the first and second load impedances are determined based on the load network.

Description

FOB WITH INCREASED POWER LEVEL FROM HAND-

ANTENNA COUPLING

BACKGROUND

[0001] A remote keyless entry system (RKE system) includes a remote device, sometimes called a fob or key fob, used by a vehicle operator in communication with a base unit embedded in the vehicle. The RKE system’s range, i.e., the possible distance between the fob operated by the vehicle operator and the base unit, is a characteristic of perceived system quality. The system’s range varies according to the fob’s radio frequency (RF) output power, and is typically designed for maximum power, and therefore maximum range, when operating in free space. An object, e.g., a person’s hand operating the fob, proximate to the antenna may reduce the output power, resulting in a reduction of range. One solution for preventing or reducing an amount of power loss caused by a hand holding the fob is to design the fob such that the antenna is in a location where it is not likely to be interfered with by the hand. However, in some fobs, due to, e.g., size limitations, this may be difficult.

SUMMARY OF TUI INVENTION

According to the present invention, there is provided a fob, comprising a power amplifier including an output having an output impedance; a radio frequency antenna connected to the power amplifier output representing a first load impedance to the power amplifier output in a space substantially free of interference for radio frequency transmissions and a second load impedance to the power amplifier output when a hand of a user is capacitively coupled to the antenna; wherein a difference between the second load impedance and the output impedance of the power amplifier is less than a difference between the first load impedance and the output impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1 is diagram of an example remote keyless entry system, including an example fob.

[0003] Figure 2 is a diagram of a transceiver for the exemplary fob of Figure 1.

[0004] Figure 3 is a diagram illustrating an exemplary coupling between a hand and a radio frequency antenna in the exemplary fob of Figure 1.

[0005] Figure 4 is a perspective view of an exemplary fob.

[0006] Figure 5A is a front end view of the exemplary fob of Figure 4.

[0007] Figure 5B is a left side view of the exemplary fob of Figure 4.

[0008] Figure 5C is a right side view of the exemplary fob of Figure 4.

[0009] Figure 5D is a bottom view of the exemplary fob of Figure 4.

[0010] Figure 6 is a perspective view of a hand holding the exemplary fob of Figure 4.

[0011] Figure 7A is a front view of an exemplary fob.

[0012] Figure 7B is a bottom view of the exemplary fob of Figure 7A.

[0013] Figure 8 is a perspective view of a hand holding the exemplary fob of Figures 7A and 7B.

DESCRIPTION

INTRODUCTION

[0014] As described above, a fob is typically designed for maximum power output in free space. Free space may be defined, with regard to an operation of the fob, as a space substantially free of interference for radio frequency transmissions. An alternate solution is to design the fob such that the fob’s output power increases due to coupling from a hand proximate to the antenna. A fob transceiver may be designed such that an electrical coupling between a hand (or other object) and the radio frequency antenna causes an improved matching between an output impedance of a power amplifier and an effective load impedance seen by the power amplifier. The improved matching may improve output power and increase the range of the fob. This may have the advantage of an easier fob design, by allowing the antenna to be disposed, e.g., in a location near to input buttons, within the input buttons, or near other areas of the fob, which are likely to be contacted by the hand (or portion of the hand, e.g., a thumb) during operation. For example, the antenna may be disposed below an outer surface of a fob, near or in the input buttons.

[0015] In the drawings, the same reference numbers indicate the same elements.

[0016] Figure 1 illustrates an example of a remote keyless entry (RKE) system 10 for a vehicle 12. The RKE system 10 provides for remote control from a fob 14 for various vehicle 12 applications such as door locks, trunk latch, interior and exterior lights, engine start, climate control, etc. The vehicle 12 is generally a land-based vehicle having two or more wheels, e.g., a passenger car, light truck, a motorcycle, etc. The vehicle 12 includes a base station 13 for receiving messages from the fob 14 and optionally transmitting messages to the fob 14.

[0017] The fob 14 transmits messages to the base station 13 and may also receive messages from the base station 13. Communications between the fob 14 and the base station 13 are typically radio frequency (RF) communications. As is known, typical fob 14 frequencies of operation for one-way communication are 315MHz or 433MHz, and for two-way communications are 902MHz or 868MHz.

[0018] The fob 14 includes a case 15 and one or more input buttons 16 for receiving inputs from an operator. The case 15 encloses electronic circuitry to facilitate radio frequency (RF) communications, as is known. The electronic circuitry includes a transceiver for transmitting RF communications to, and in the case of two-way communications, receiving RF transmissions from, the vehicle 12. The transceiver includes one or more antennas 17, which may be disposed, as described below, in the case 15. Additionally, the fob 14 includes a ground plane 18. When under power, i.e., when a battery or direct current power supply is connected to the electronic circuitry, the ground plane 18 is at ground potential, typically zero volts. As discussed below, the ground plane 18 may have one or more coupling portion 18a, for coupling with a hand of the operator. The coupling portion 18a may be, e.g., embedded in the case 15.

[0019] As shown in Figure 2, an exemplary transceiver 20 for the fob 14 includes a power amplifier 24, one or more antennas 17, and, in implementations in which the transceiver 20 is configured for two-way communications, a receiver 22. The transceiver 20 may further include, e.g., a load network 26. The load network 26 may include one or more passive components, e.g., resistors, capacitors, inductors, etc., and may be connected, for example, from an output of the power amplifier to the ground plane 18.

[0020] The receiver 22 may receive radio frequency (RF) signals from, e.g., the vehicle 12 via the antenna 17. Based on the received RF signals, the receiver 22 may generate a received signal which is output, for example, to a computer included in the fob 14.

[0021] The power amplifier 24 receives a transmission signal, e.g., from a radio frequency signal generator, as is known, then increases a power level of the transmission signal, and outputs the increased power level transmission signal to the RF antenna 17.

[0022] The power amplifier 24 is characterized by an output impedance. The output impedance may have an ohmic component, and may additionally have a reactive component. For example, a value of the output impedance for the power amplifier may be nominally 50 Ohms. The impedance may include a frequency dependent reactive component, due to, e.g., inductance in wires connecting the output amplifier to the antenna 17. For example, a wire with 20nH of inductance has an impedance of approximately j 50 Ohms at a frequency of 400MHz.

[0023] The one or more antennas 17 transmit RF output signals to the vehicle 12, and in the case of two-way communications, receive RF input signals from the vehicle 12. The antenna 17, together with the load network 26, may present a load impedance to the power amplifier 24.

[0024] A matching of the load impedance presented to the output amplifier 24 and the output impedance of the power amplifier 24 affects the output power of the transceiver 20. A maximum output power level is obtained when the load impedance matches the output impedance of the power amplifier 24. However, the load impedance may be influenced by the presence of a hand operating the fob 14.

[0025] As shown in Figure 3, a hand 32 operating the fob 14 may be electrically coupled to the antenna 17. For example, a first capacitive coupling 34a may be formed between the antenna 17 and the hand 32. A second capacitive coupling 34b may be formed between the hand 32 and the ground plane 18. The combination of the first capacitive coupling 34a and second capacitive coupling 34b, may electrically couple the hand 32to the antenna 17 such the load impedance presented to the power amplifier 24 is changed.

[0026] In order to maximize the output power of the transceiver 20, the load impedance of the antenna 17 and load network 26 may be selected such that the change of load impedance due to the presence of the hand 32 improves the matching between the load impedance and the output impedance of the power amplifier 24.

[0027] The capacitive coupling 34a of the hand 32 to the antenna 17 may vary, depending on a first distance of the hand 32 from the antenna 17. Similarly, the capacitive coupling of the hand 32 to the ground plane 18 may vary depending on a second distance between the hand 32 and the ground plane 18. In order to reduce the effects of this variation, the fob 14 case 15 may be dimensioned and the components arranged such that the variation of distance of the hand 32 to the antenna 17 and ground plane 18 are minimized.

[0028] For example, as further discussed below, one or both of the antenna 17 and a coupling portion 18a of the ground plane 18, may be embedded in the case 15, respectively a first and second predetermined distance below an outer surface of the case 15. The first and second predetermined distances may each be, for example, 1 millimeter. The antenna 17 and coupling portion 18a of the ground plane 18 may similarly be disposed in the case 15 near a location which is likely to be in contact with the hand 32 during operation of the fob 14.

[0029] For example, one or both of the antenna 17 and coupling portion 18a of the ground plane 18 may be disposed within respective third and fourth predetermined distances from the buttons 16 used to operate the fob 14. The third and fourth predetermined distances may be, for example, 0.5 centimeters. Additionally or alternatively, for example, one or both of the antenna 17 and coupling portion 18a of the ground plane 18 may be disposed on a surface of the fob 14 opposite the buttons 16, where an operator is likely to apply counter pressure during operation of the buttons 16. Other examples are presented below.

[0030] An exemplary fob 14 is shown in Figures 4 and 5A-5D. The fob 14 includes the case 15. The case 15 may be generally in the form of a rounded, rectangular box, forming an internal cavity. The internal cavity encloses the transceiver 20, and other electronic circuitry, to facilitate radio frequency communications, as discussed above. The case 15 includes an interface portion 41, a handle portion 42, a top surface 47 and a bottom surface 48 (Figure 5D). The case 15 may, for example, be formed of a hardened plastic or other non-conductive material.

[0031] The interface portion 41 includes left lateral side 43, right lateral side 44, and a front end 46, and may further include one or more input buttons 16. The one or more input buttons 16 may be disposed on the top surface 47, and include, for example, first, second, third and fourth input buttons 16a, 16b, 16c, 16d.

[0032] At least one antenna 17 may be disposed on the interface portion 41. The antenna 17 may be, e.g., a wire embedded within, e.g., the top surface 47 and/or bottom surface 48.

[0033] The capacitive coupling 34a between the hand 32 operating the fob 14 and the antenna 17 depends on a distance between the hand 32 and the antenna 17. In order to increase a predictability of the capacitive coupling 34a, the antenna 17 may be located a predetermined distance below an outer surface of the fob 14. The predetermined distance may be, for example, one millimeter. The predetermined distance may be chosen based on the value of the capacitive coupling 34a that is desired, based on manufacturing tolerances, etc. For example, as shown in

Figure 4, the antenna 17 may be disposed near a top surface 47, within the hardened plastic or other non-conductive material used to form the case 15.

[0034] Additionally, the antenna 17 may be located, e.g., in a position near or in between the input buttons 16. As shown in Figure 4, the antenna 17 may be located between bottom edges 55a, 55b respectively of the first and second buttons 16a, 16b, and a top edge 56 of the third button 16c. As another example, the antenna 17 may be disposed below a bottom edge 57 of the third input button 16c and above a top edge 58 of the fourth input button 16d. In each of these examples, a likelihood that a thumb on the hand 32 will be near to the antenna 17 is high, during an activation of one of the buttons 16. Because the buttons 16 are suppressed during activation, a variation in a distance between the thumb and the antenna 17, due to, e.g., holding the fob 14 in different orientations may be minimized.

[0035] In order to increase the predictability of the capacitive coupling 34b between the ground plane 18 and the hand 32 operating the fob 14, the ground plane 18 may include a coupling portion 18a. The coupling portion 18a may be for example, a metal plate or wire electrically connected to the ground plane, and may be disposed in the case 15. The coupling portion 18a of the ground plane may be located a predetermined distance, e.g., one millimeter, below an outer surface of the fob 14. The predetermined distance may be chosen based on the value of the capacitive coupling 34b that is desired, based on manufacturing tolerances, etc. As shown in Figure 4, the antenna 17 may be disposed near a top surface 47, within the hardened plastic or other non-conductive material used to form the case 15.

[0036] The antenna 17 and coupling portion 18a of the ground plane 18 may be disposed in other locations within the fob 14. For example, as shown in Figures 5B, 5C and 5D, the antenna may be disposed on a left side 43, 50, on a right side 44, 52, and/or on the a bottom surface 48 of the fob 14. For example, a finger groove 60 (Figure 5D) may be formed in the bottom surface 48, and the antenna 17 may be disposed in the finger groove 60. As described above, the antenna 17 may be disposed a predetermined distance, for example one millimeter, below the bottom surface 48.

[0037] Similarly, the coupling portion 18a of the ground plane 18 may be disposed, for example, on the bottom surface 48, at a location opposite the input buttons 16.

[0038] In order to increase predictability of the capacitive coupling 34b between the coupling portion 18a of the ground plane 18 and the hand 32 operating the fob 14, the coupling portion 18a of the ground plane 18 may be located, e.g., in a position near the input buttons 16. As one example and as shown in Figure 4, the coupling portion 18a of the ground plane 18 may be located below a bottom edge 59 of the fourth input button 16d. This is an area where the thumb operating the fob 14 is likely to cross over or touch during operation of the fob 14 (see, e.g., Figure 6).

[0039] As further shown in Figure 4 and 5A-5D, the case 15 includes a handle portion 42. The handle portion 42 extends from a side of the interface portion 41 opposite the front end 46 in the direction of a center axis 51 and has left and right lateral sides 50, 52.

[0040] The predictability of the respective values of the capacitive coupling 34a between the hand 32 and the antenna 17, and the capacitive coupling 34b between the hand 32 and the ground plane 18, may be increased by forming the fob 14 to direct an orientation of the hand 32 holding the fob 14. For example, the fob 14 handle portion 42 may include one or more finger positioners 53. The finger positioners 53 may be, for example, one or more grooves formed in each of the left and right lateral sides 50, 52 of the handle portion 42. The grooves may have a shape that corresponds to a shape of at least a portion of a human finger, e.g., an inside (palm side) of the finger. In the case that there is more than one finger positioner 53, the finger positioners 53 may be arranged adjacently, with a spacing corresponding to the spacing of fingers on the human hand 32. The grooves may direct an operator of the fob 14 to hold the fob 14 such that fingers of the hand 32 are placed in the grooves 53. In this manner, a thumb of the hand 32 may naturally extend from the handle portion 42 toward the interface portion 41. As described above, the antenna 17 and coupling portion 18a of the ground plane 18 may be disposed on the fob 14 such that the thumb is passes over them when the fob 14 is operated in a directed orientation.

[0041] A shape of the bottom surface 49 of the fob 14 case 15 may also be used to direct the orientation of the hand 32 when operating the fob 14. For example, as shown in Figure 5D, the bottom surface 48 may include a finger slot 60. The finger slot 60 may be a groove formed in the bottom surface 48 and shaped to receive a finger. The finger slot 60 on the bottom surface 48 may be aligned, e.g., with one of the finger positioners 53 formed in the left and right lateral sides 50, 52. In the case where there is more than one finger positioner element 53 formed in the left and right lateral sides 50, 52, the finger slot 60 in the back surface 48 may be aligned with the finger positioner 53 nearest the interface portion 41. This position corresponds to a position of an index finger holding the fob 14 in a directed orientation. In the directed orientation, the other fingers of the hand of the operator holding the fob 14 are placed on the handle portion 42 on a side of the finger slot 60 opposite the interface portion 41.

[0042] Figure 6 illustrates the example fob 14 of Figures 4 and 5A-5D, being held in the directed orientation. The fingers are directed to hold the fob 14 at the handle portion 42 by the finger positioners 53. The index finger of the hand is directed to the finger slot 60 on the bottom surface 49 (Figure 5D). As shown, there are multiple locations where an antenna 17 may be placed such that the thumb of the hand 32 is near the antenna 17 during operation of the fob 14. Similarly, an ground plane coupling portion 18a may be placed, e.g., on the top surface 47 of the handle portion 42, such that the thumb is near to the ground plane coupling portion 18a.

[0043] A second exemplary fob 114 is shown in Figures 7A and 7B. The fob 114 includes a case 115 which has a top surface 147 and a bottom surface 148. The fob 114 further includes one or more inputs 16, one or more antennas 17 as described above with reference to the fob 14. The fob 114 further includes the transceiver 20, as shown in Figure 2. The transceiver section 20 is connected to and receives its electrical ground connection from the ground plane 18. Also, as described with regard to the fob 14, the ground plane 18 may include a coupling portion 18a, which is electrically connected to the ground plane 18, and, e.g., embedded within the case 115.

[0044] The fob 114 may be, formed within a handle portion of a key, and may be relatively small. For example, a length of the fob 114 may be substantially five centimeters. Due to this relatively small size, most areas of the fob 114 will be in direct or near contact with the hand 32 holding the fob 114 during operation. Including the predicted electrical coupling 34a of the hand 32 with the antenna 17 may have the advantage of more options for placement of the antenna 17 within the fob 114.

[0045] As shown in Figure 7A, an antenna 17 may be placed, for example on the top surface 148, in between one or more of the inputs 16. Additionally or alternatively, the antenna 17 may be placed within one of the inputs 16. As described above, the antenna 17 may be embedded in the casing, a predetermined distance, e.g., one millimeter, below the top surface 147.

[0046] As further indicated in Figure 7B, in order to increase the predictability of the coupling 34b between the hand 32 and the ground plane coupling portion 18a may be embedded a predetermined distance below the bottom surface 148 of the fob 114. The predetermined distance may be, e.g., one millimeter.

[0047] Figure 8 illustrates the example fob 114 of Figures 7A and 7B, being held by a hand 32 in a natural position. The thumb extends over a substantial portion of the top surface 147, and the fingers cover a substantial portion of the bottom surface 148 (see Figure 7B). Accordingly, there are multiple options on the top surface 147, on the bottom surface 148, and within the inputs 16 for placement of the antenna 17 and, when utilized, the ground plane coupling portion 18a, such that a respective capacitive coupling 34a, 34b, is formed.

[0048] The placements of the antenna 17 and the ground plane coupling portion 18a discussed herein are only examples. The antenna 17 may be placed in any location on the fob 114 where a strong coupling with the hand 32 may be formed during operation of the fob 114. Similarly, the coupling portion 18a of the ground plane 18 may be placed in any location on the fob 114 where a strong coupling with the hand 32 may be formed. Note that, with regard to the ground plane 18, a coupling portion may not be necessary. The ground plane 18 may be distributed substantially through the fob 114, such that a sufficient coupling is formed without the provision of the ground plane coupling portion 18a.

[0049] As used herein, the adverb “substantially” means that a shape, structure, measurement, quantity, time, etc. may deviate from an exact described geometry, distance, measurement, quantity, time, etc., because of imperfections in materials, machining, manufacturing, etc.

[0050] The term “exemplary” is used herein in the sense of signifying an example, e.g., a reference to an “exemplary widget” should be read as simply referring to an example of a widget.

Claims

1. A fob, comprising: a power amplifier including an output having an output impedance; a radio frequency antenna connected to the power amplifier output representing a first load impedance to the power amplifier output in a space substantially free of interference for radio frequency transmissions and a second load impedance to the power amplifier output when a hand of a user is capacitively coupled to the antenna; wherein a difference between the second load impedance and the output impedance of the power amplifier is less than a difference between the first load impedance and the output impedance.

2. The fob of claim 1, further comprising: an electrical load network connected between the power amplifier output and a reference electrical potential, wherein each of the first and second load impedances is determined in part based on the load network.

3. The fob of claim 2, wherein the reference electrical potential is a ground potential.

4. The fob of claims 1 to 3, further comprising: a case having an outer surface; wherein the radio frequency antenna is embedded in the case and disposed a first predetermined distance below the outer surface.

5. The fob of claim 4, wherein the outer surface includes a top portion including at least one input button, and the radio frequency antenna is disposed a second predetermined distance from the input button.

6. The fob of any preceding claim, further comprising: a case having an outer surface, wherein the outer surface includes an upper portion including at least one input button, and the radio frequency antenna is disposed in the button.

7. The fob of claim 6, wherein the input button has an upper surface, and the radio frequency antenna is disposed a third predetermined distance from the upper surface of the input button.

8. The fob of any preceding claim, further comprising: a case having an outer surface; and a ground plane that provides a ground reference potential for the power amplifier when the fob is under power, the ground plane including a coupling portion, wherein the coupling portion is disposed within the case.

9. The fob of claim 8, wherein the coupling portion is disposed a fourth predetermined distance from the outer surface of the case.

10. The fob of any preceding claim, wherein the fob further comprises: at least one hand positioning element arranged to orient an operator’s hand on the key fob toward the antenna.

11. The fob of claim 10, wherein the at least one positioning element includes at least one finger positioner.

12. The fob of claim 11, wherein the fob further comprises: a case having an outer surface, the outer surface having a top portion and a bottom portion opposite the top portion; at least one input arranged on the top portion of the outer surface; and a finger slot formed in the bottom portion of the outer surface; wherein the antenna is embedded in the case, and within the finger slot.